Paraconformity A paraconformity is a type of unconformity in which strata are parallel; there is no apparent erosion and the unconformity surface resembles a simple bedding plane. It is also called nondepositional unconformity or pseudoconformity. Short paraconformities are called diastems.
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The contact of the Shinumo Quartzite with the Hakatai Shale is the only documented unconformity that has been found within the Unkar Group. This unconformity truncates across beds and channel deposits of the Hakatai Shale. The relief at this unconformity is small, being about . The Shinumo Quartzite overlying this unconformity consists of arkosic conglomeratic sandstone that contains quartzite and granite pebbles.
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The Calcare di Altamura overlies the Calcare di Bari, separated by an unconformity and is overlain by the Calcare di Caranna, separated by a transgressive angular unconformity.
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The Taconic Unconformity, near Catskill, NY The Taconic unconformity is a major unconformity created during the Taconic orogeny, exposed from eastern New York State to the Gaspe peninsula.Skidmore, W. B. "The Taconic unconformity in the Gaspe Peninsula and neighbouring regions." Royal Society of Canada, Special Publication 10 (1967). The orogeny was a long one that comprised multiple bursts; it primarily dated to the end of the Ordovician, and the underlying rocks are primarily this age.
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An unconformity occurs before late Miocene sequences including the Dupi Tila sandstone and claystone, with another unconformity between the Dupi Tila units and Pliocene Dihing claysone and silty sandstone. Pleistocene St. Martin's limestone and Madhapur clay are separated from Pliocene units by an unconformity as well from Holocene sand, silt, clay, peat and coral alluvium.
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The horizontal Tonto Group units are laid upon the Vishnu Basement Rocks above an angular unconformity as the Vishnu Basement Rocks have a dip of about 15 degrees. This erosion unconformity prior to the deposition of the Tapeats upon the tilted Vishnu Basement Rocks is about 1,000 million years (1.0 billion years), and is called the Great Unconformity.
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The Tapeats unit is the bottom member of the Tonto Group, a typical marine transgression series of sandstone-(conglomerate)-shale- limestone, all part of a paleo sea, initially adjacent to land, the source of the Tapeats rocks-(conglomerates) and sand; (a regressing sequence has the reverse order). The Tapeats Sea at the early Devonian ceased to deposit more Muav Limestone, and a period of erosion ensued, a deposition unconformity. The Tapeats Sandstone was laid upon the Vishnu Basement Rocks, after an unconformity of erosion, the Great Unconformity, of 1,000 million years (1.0 billion). Besides the erosion unconformity, the Unkar Group of the basement rocks are also at an angular unconformity, being an 8-member sequence tilted at 45 degrees.
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These Ordovician rocks lied on top of the Cambrian rocks without unconformity.
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Beginning with the 1st sequence, the lithologies are consistent with the formation of the basin along with the volcanic arc, the deposition of the volcanic arc sediments, and ultimate uplift of the basin region, which causes the erosional unconformity. The 2nd sequence stratigraphy displays a marine transgression, and ends with an erosional unconformity. This unconformity could be caused by subaerial erosion due to a regression following the transgression, but it is unknown because that stratigraphy has been eroded. The 3rd sequence shows a marine transgressive event following the previous unconformity, leading into the present day.
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The Cromer Knoll is deposited on top of an unconformity at the base of the Cretaceous period. Regional uplift and erosion allowed the unconformity to appear in the late Triassic and depositing the Cromer Knoll and chalk groups.
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The upper contact, which is part of the Great Unconformity, of the Sixtymile Formation is a disconformity that laterally becomes an angular unconformity. Within the center of Chuar syncline, this upper contact is a disconformity. Away from the center, the strata of the Sixtymile Formation, an angular discordance between the formations of 6° to 10° can be seen. The Great Unconformity has an irregular hilly surface.
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A proto rift unconformity also develops in this situation as seen in the southern and central parts of the palaeorift system where domal structures were deeply eroded in the middle Jurassic which is known as the 'Mid-Cimmerian' unconformity.
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Sedimentary rocks of Ordovician age cover this surface making it largely an unconformity. At parts the unconformity of the Precambrian basement has glacial striations, rôche moutonnées and chatter marks formed likely during the Karoo Ice Age. The Paleozoic sedimentary cover above the unconformity is of fluvial and glacial origin (Enticho Sandstone, Edaga Arbi Glacials). Early Jurassic marine sediments cover much of the older sediments including a planation surface of Triassic age.
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Hutton's Unconformity The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in a region. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of geologic time not represented is called a hiatus.
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It is in turn overlain by the Lohan Cura Formation, separated by another unconformity.
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Hutton's Unconformity at Jedburgh, Scotland, illustrated by John Clerk in 1787 and photographed in 2003. An unconformity is a buried erosional or non- depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity (see below) was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in 1788.
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After the middle Miocene, there lies an unconformity which represents a ~10 million year depositional hiatus.
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The unconformity that separates the basement from the first sequences indicates the approximate time rifting began.
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Beneath the McGrath, and separated by an unconformity, portions of the Miocene-age Santa Margarita and Monterey Formations show in drilling logs; yet another unconformity marks the top of the Colonia Zone, of Oligocene age, which contains more lenticular and pinched-out reservoirs of oil sands.
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51(8): 1235–69. The contact between the Tonto Group and Unkar Group is a prominent angular unconformity, which is part of the Great Unconformity. The surface of this angular unconformity truncates dipping strata comprising the folded and faulted Unkar Group. Though this surface is typically a plane, differential erosion of the tilted strata of the Unkar Group left resistant beds of the upper layer Cardenas Basalt and the middle layer Shinumo Quartzite as ancient hills, called monadnocks.
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A buttress unconformity occurs when younger bedding is deposited against older strata thus influencing its bedding structure.
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The deposit is a Carlin–type gold deposit, similar to those found in the Carlin Unconformity, Nevada.
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The overall history of the Rub' al Khali Basin goes back to the Proterozoic ("Precambrian"). The first regional tectonic signature in the history is recorded as the end-Ediacaran unconformity, followed by the pre-Siq unconformity affecting the western and southwestern edges of the basin.Jaju et al., 2016, p.
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The hill ranges of the Tirumala rise to a height of (at Tirumala) from the average height of in the plains at Tirupati. The steep scarp of the hill ranges depicts unconformity in its topographic, structural and denudational features, which is the Eparchian Unconformity. The sedimentary thickness of the Cudappa basin is of the order of with volcanic sequences in the form of sills and dykes. A prominent Eparchaean Unconformity of the formation resting on the Archaean peninsular gneissic complex is noted.
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Geologist John Wesley Powell called this major gap in the geologic record, which is also seen in other parts of the world, the Great Unconformity. Other sediments may have been added but, if they ever existed, were completely removed by erosion. Such gaps in the geologic record are called unconformities by geologists. The Great Unconformity is one of the best examples of an exposed nonconformity, which is a type of unconformity that has bedded rock units above igneous or metamorphic rocks.
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Angular unconformity An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole sequence may later be deformed and tilted by further orogenic activity. A typical case history is presented by the paleotectonic evolution of the Briançonnais realm (Swiss and French Prealps) during the Jurassic.Septfontaine M. (1984): Le Dogger des Préalpes médianes suisses et françaises - stratigraphie, évolution paléogéographique et paléotectonique.
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In geology, a subaerial unconformity is a surface that displays signs of erosion by processes that commonly occur on the surface. These processes generating the subaerial unconformity can include wind degradation, pedogenesis, dissolution processes such as karstification as well as fluvial processes such as fluvial erosion, bypass and river rejuvenation.
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This formation is capped by the breakup unconformity signifying the transition from syn- to post-rift around 32 Ma.
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The stratal geometries that are characteristic of the unconformity depend strongly on structural and geographical position within the basin.
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This may be a result of large variation in clast size as with the upper Pliocene Pico Formation in the northwestern part of the basin and the Upper Fernando Formation in the southwest part of the basin. The Los Angeles Basin contains what is known as the "Great Unconformity" which has been interpreted as a large scale erosional event in the basement rock unit. This unconformity is used to correlate strata throughout the basin. The record of the Cenozoic activity begins above this unconformity.
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The Safonovo Group upward end is an unconformity that separates it from the poorly sorted sandstones of the Uftuga Formation.
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The seals in this region are mainly marl, limestone, and sandstone from the Seaspray Group. These rock types are aided by being deposited on the Latrobe unconformity. This unconformity is due to the anticlines that formed in the Latrobe group being eroded, and then the Seaspray group being deposited on top of this erosional surface.
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Surprise Canyon was unknown to science until 1973 and can be reached only by helicopter. Fossil logs, other plant material and marine shells are found in this formation. An unconformity marks the top of the Surprise Canyon Formation and in most places this unconformity has entirely removed the Surprise Canyon and exposed the underlying Redwall.
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Hutton's Unconformity is a name given to various notable geological sites in Scotland identified by the 18th-century Scottish geologist James Hutton as places where the junction between two types of rock formations can be seen. This geological phenomenon marks the location where rock formations created at different times and by different forces adjoin. For Hutton, such an unconformity provided evidence for his Plutonist theories of uniformitarianism and the age of the Earth. An unconformity is any break in the normal progression of sedimentary deposits, which are laid the newer on top of the older.
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The contact between the overlying Tapeats Sandstone and the folded and faulted Nankoweap Formation is a prominent angular unconformity that is part of the Great Unconformity. Uranium-lead dating of detrital zircons from the Nankoweap Formation indicate the presence of zircon grains in approximately the 800-770 Ma age range. This finding indicates that the Nankoweap Formation is closely related in age and stratigraphy to the Chuar Group - and any unconformity associated with its upper contact is relatively minor in duration and significance. Thus, the Nankoweap Formation is most likely the basal unit of the Chuar Group.
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The Tippecanoe comprises the St. Peter Sandstone, Joachim Dolomite, Plattin Limestone, Decorah Shale, Kimmswick Limestone, and an unconformity, followed by the Girardeau Limestone (only in the southeast), Maquoketa Shale and northeast Missouri Noix Limestone. Silurian Tippecanoe rocks include only two units: the Bainbridge Formation in the southeast and Bowling Green Dolomite in the northeast. Devonian Kaskaskia rocks include the Chattanooga Shale in the southwest, Cedar Valley Limestone, split by an unconformity and separated from Mississippian rocks by a second unconformity, with numerous small shale and limestone units in the east. A complicated sequence of shale, sandstone and limestone follows from the Carboniferous.
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Muav Limestone cliff example, below Redwall Limestone cliff, on the North Kaibab Trail (closeup photos, often show purple erosion debris) (expandable photo) The Tonto Group units were deposited on an ancient erosion surface (angular unconformity) on the Vishnu Basement Rocks. The Vishnu sequence has a dip of about 45 degrees. As this long-timeframe unconformity represents about 1,000 million years (1.0 billion years) of non–deposition, tectonic activity and erosion, on the Vishnu Basement Rocks, is called the Great Unconformity. Beyond the Grand Canyon area the Muav occurs in southern Utah, southern Nevada and southern California.
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The Mid-Carboniferous unconformity is an unconformity located in many countries, such as England (Namurian Series), Thailand, The United States and more. It has been dated to the Namurian, Middle Carboniferous (c.326-313 Ma) and the formation is often noted as being similar to the mid-Carboniferous eustatic event.Gradstein, Felix M.; Ogg, James G.; Smith, Alan G., eds. (2004).
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The basal conglomerates are made up of hard sandstone which contains angular grains. At Alderley Edge the junction is quite sharp it could be regarded as an unconformity. However interdigitation is found as if to testify against an unconformity. Mappable beds showing all the characteristics of the Upper Mottled Sandstone are found between the two basal beds of the conglomerates.
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Lummaton Quarry's shell deposits led to the naming of the Devonian period. Saltern Cove is a regionally important unconformity and Site of Special Scientific Interest.
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The formation overlies across an angular unconformity older sedimentary rocks of continental origin as well as dykes and plutons that intruded these sediments. The unconformity has an irregular form attesting to a topography that was flattened out by the deposition of the Cola de Zorro sediments. Cola de Zorro Formation was deposited in Pliocene and Pleistocene times. The formation interdigitates with lavas of old and eroded volcanoes.
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The first phase of rifting ceased in the Albian at which time the basin underwent an erosive compressional period leading to the basin wide Otway unconformity.
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A series of outcrops occur from East Lothian southwards through Berwickshire. Hutton's famous unconformity at Siccar Point occurs within this basin - see History of study below.
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These rocks of the Borrowdale Volcanic Group give rise to dramatic scenery. The mountainous nature of the area, its high rainfall and the relative impermeability of the rock give rise to a high risk of storm flooding as demonstrated by the 2009 flooding of Cockermouth. The upper boundary of the group is an unconformity with the overlying Windermere Supergroup. The lower boundary is an unconformity with the underlying Skiddaw Group.
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The stratigraphy of Bangladesh begins with Precambrian units below ground. Geologists have found an unconformity between Precambrian and Paleozoic units. Gondwanan sedimentary units, including the early Permian Kuchma and late Permian Paharpur range between 494 meters and 1.2 kilometers in thickness. Ascending the stratigraphic column, a second unconformity separates Permian units from late Jurassic Rajmahal basalts and early Cretaceous Sibganj sedimentary rocks, with thicknesses between 131 and 546 meters.
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The group is made up of four formations, from youngest to oldest these are: Millongue Formation, Trihueco Formation, Boca Lebu Formation and Curanilahue Formation. The Eocene Millongue Formation is composed of shale and siltstone of both marine and continental origin. Its top is marked by an unconformity, the so-called “main unconformity” of Arauco Basin, which is thought to have formed by erosion during a period of tectonic inversion.
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Well-bedded Torridonian sandstone The Torridonian is a sequence of Neoproterozoic sediments, mainly sandstones that rest unconformably on an old land surface, with up to 300 m of relief locally. The Torridonian is divided into the older Stoer Group and the younger Sleat and Torridon Groups separated by an angular unconformity. Paleomagnetic data suggest that this unconformity represents a major time break. These sediments are interpreted to have been deposited during a period of rifting.
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Above the Pre-Neogene sequence lies a major unconformity, overlain by early Miocene rocks. This unconformity is the result of the area being subjected to subaerial erosion, but then was followed by a marine transgression, which deposited the overlaying Miocene rocks. This transgression originally deposited near-shore sands, followed by shallow water siltstones. Towards the middle Miocene, the region developed into a carbonate shelf, and these carbonates make up the rest of this sequence.
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An angular unconformity truncates progressively older (lower) parts of the underlying Pahrump Group starting in the southern part of the area and moving north. At its northernmost extent, the unconformity in fact removed all of the Pahrump, and the Noonday rests directly on the Proterozoic Complex. An ancient period of erosion removed that part of the Pahrump due to its being higher (and thus more exposed) than the rest of the formation.
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An unconformity separates the basin from the Blue Hills in the northeast where it tapers out. The Pondville Conglomerate, lying atop the Blue Hill Granite Porphyry dips 60 degrees south.
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The land to the west (around Wagga Wagga) was raised higher. An unconformity resulted between the Pittman Formation and the State Circle Shale and Black Mountain Sandstone deposited on top.
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The Elephant Canyon Formation is the basal Permian geologic formation of the Cutler Group overlying an unconformity on the Pennsylvanian Honaker Trail Formation in the Paradox Basin of southern Utah.
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A blended unconformity is a type of disconformity or nonconformity with no distinct separation plane or contact, sometimes consisting of soils, paleosols, or beds of pebbles derived from the underlying rock.
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The whole sequence sits on an unconformity with the underlying Liantuo formation, which is free of fossils, an unconformity usually being interpreted as a period of erosion. On that unconformity lie tillites of the Nantuo formation - cemented glacial till formed of glacial deposits of cobbles and gravel laid down at the end of the Marinoan glaciation (also known as Varangian glaciation, this is the second and last of a series of very extensive glaciations during a period called the Cryogenian -- named because 'Snowball Earth' conditions at the time). This latest Cryogenian glacial level is tentatively dated ca 654 (660 ± 5) — 635 Ma (million years ago). The Doushantuo formation itself has three layers representing aquatic sediments that formed as sea levels rose with the melting of worldwide glaciation.
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Gondwana Strata of LHS in Western and Central Nepal In Nepal, the older LHS with age ranging from the Paleoproterozoic to uppermost Precambrian are separated from the younger LHS by the Great Lesser Himalayan Unconformity. Missing Early Proterozoic strata of the LHS suggest that the rocks may have been eroded before the deposition of the Gondwana strata. Younger continental facies Gondwana strata were first deposited after the unconformity. They are then unconformably overlain by a marine facies Tertiary Unit.
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Scottish Geology – Hutton's Section at Salisbury Crags Scottish Geology – Hutton's Rock at Salisbury Crags He found other examples in Galloway in 1786, and on the Isle of Arran in 1787. Hutton's Unconformity on Arran Hutton Unconformity at Jedburgh. Photograph (2003) below Clerk of Eldin illustration (1787). The existence of angular unconformities had been noted by Nicolas Steno and by French geologists including Horace-Bénédict de Saussure, who interpreted them in terms of Neptunism as "primary formations".
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The presence of Potassium felspar indicates arid conditions were prevalent at the time. During the Olenekian the average temperature was in the low 30s, and the rainfall was less than 180 mm per year. Also part of the Iberian Basin is the Castilian Branch. Formation in this are from the Permian: Boniches, Alcotas, an unconformity followed by Hoz de Gallo Conglomerate, this is capped by sandstone and silcrete at another unconformity marking the end of the Permian.
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In its upper part the river runs through a valley cut into horizontal beds of Carboniferous Great Scar limestone. At Thornton Force it crosses a notable unconformity into the underlying, steeply inclined Ordovician greywackes. The unconformity is clearly visible in the face of the waterfall. The Ordovician strata influence the character of the steep and narrow Swilla Glen and its waterfalls until, just north of Ingleton, the river crosses the Craven Fault and onto Carboniferous Limestone once again.
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After the deposition a period of uplift and erosion occurred due to the further expansion and rifting of the Atlantic Ocean that forms an unconformity at the top if the middle Kimmeridgian deposits.
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The fourth order might be controlled by large scale glaciation and global ocean patterns over the course of a million years.Chang, K.H., (1975). Unconformity-bounded stratigraphic units. Geological Society of America Bulletin, v.
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They are overlain by unmetamorphosed carbonates from the late Silurian through the middle Devonian, with an angular unconformity at the base. Another angular unconformity above separates these rocks from volcanic and continental sedimentary rocks, with thick conglomerate at the base, ascending to pebbly limestone and metamorphic rocks. The upper unit is a thick cooled lava and tuff overlain by sandstone, conglomerate and Carboniferous plant remnants. The tectonic zone to the north has greater meta-pelagic rock presence and rare fossils from the Cambrian.
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Any angular unconformity is prove that a tectonic phase took place between the deposition of the layers below and on top of it. It is important to know if the tectonic phase was a longer event or if it was local or regional. Tectonic phases can be important events that affected large areas. The Alleghenian orogeny in North America (during the Carboniferous period) for example can be found as an angular unconformity between rock layers in large parts of that continent.
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The unconformity that cuts across the Marañón fold and thrust belt show the Incaic Phase of the Andean orogeny ended no later than 33 million years ago in the earliest Oligocene. Above this unconformity the belt is overlain by volcanic rocks of Late Eocene to Miocene age. The parts of the belt are intruded by plutons of the Coastal Batholith of Peru. There are various mineralizations of base metals and precious metals in the belt, being particularly common along Chonta Fault.
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The Hercynian orogeny affected the Middle East Craton in the Late Carboniferous, driving erosion and warping. Clastics deposited on the unconformity left by the erosion through the Permian, principally sandstone, siltstone, anhydrite and dolomite.
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Currently, the Sabine Uplift is in the subsurface, and the middle Cretaceous unconformity is not seen because it is buried below a massive wedge of clastic sediments from the Late Cretaceous to the present.
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The exposures shows the unconformity between the Lower Blaisdon Beds (top) and the Gorstian Upper Flaxley Beds. The site is a key stratigraphic locality for research of the Ludlow Series rocks of May Hill.
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In southwest Skåne, the Rya Formation is missing or only poorly developed.Ahlberg et al., 2003, p.533 In the Øresund Basin between Sweden and Denmark, the formation is truncated by the Basal Middle Jurassic unconformity.
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This entire middle sequence indicates a marine megacycle consisting of five transgressive- regressive cycles. The angular unconformity between the second and third sequences is a result of erosion from the accretion of the Western Ranges.
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The corresponding unconformity, which exists only in the western Pyrenees, belongs to an early deformation phase of the Variscan orogeny (Breton Phase). Only in the western Pyrenees is the Lower Carboniferous (Mississippian) distinguished from the Devonian sediments by an unconformity, starting off marine with a transgressive quartz–pebble bed. Anywhere else, the Supragriotte limestones are conformably overlain by pre- orogenic sediments that begin with the Lower Cherts of the Tournaisian. The Lower Cherts comprise 50 m of black, phosphate nodule-bearing cherts interlayered with black shales.
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The Cadomin Formation overlies a major regional unconformity caused by pre-Cadomin erosion, although little or no evidence of the angular nature of that unconformity is apparent at most outcrops. It rests unconformably on the Fernie Formation, the Nikanassin Formation, the Minnes Group or the Kootenay Group, depending on the location and the extent of the erosion. It is conformably overlain by the Gladstone Formation in Alberta and Gething Formation in northeastern British Columbia, and it is equivalent to the base of the Mannville Group.
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Bosellini et al.. (1994)Bosellini A., Morsilli M. (1997). A Lower Cretaceous drowning unconformity on the eastern flank of the Apulia Platform (Gargano Promontory, southern Italy). Cretaceous Research 18: 51–61. Belfast.Morsilli M., Bosellini, A. (1997).
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Another 10 million years of erosion is marked by an unconformity. Through the Permian, salt and red bed formations filled the Williston Basin belonging to the Opeche and Spearfish formations, along with the Minnekahta Formation limestone.
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Next comes the Middle Carboniferous Bashkirian Stage limestones, and then the Lower Permian Artinksian Stage argillaceous sediments. The carbonate buildup is up to 4 km thick and form an angular unconformity to the overlying Permian sediments.
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It is divided into a lower Raydale Dolomite Formation which is overlain by the Marsett Formation and then by an upper Penny Farm Gill Formation.Its base is everywhere an unconformity with Ordovician and Devonian rocks beneath.
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2 - 0.6 ka: Unconformity. The gap between 6 - 2 ka could be attributed to shallow lake conditions. In addition, sediment types observed in the core between 2 - 0.6 ka largely reflected shallow water conditions.Newton, M. S. (1994).
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The formation overtops the Miocene Tagpochau rocks with an angular unconformity. Talus, marsh sediments and limestones such as the Mariana Limestone are common across the surface, resulting from deposition and mass-wasting during the Pleistocene and Holocene.
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The Weifang Group contains dark phyllite and limestone with Didymograptus graptolite fossils. The Luofengxi Group contains metamorphosed sandstone in which Leiomarginata and Conochitina incerta fossils have been found. During the Silurian and early Devonian an unconformity formed.
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Locally, the contact is a low relief erosional surface associated with a thin weathering zone developed in the lavas of the Cardenas Basalt. Along the length of the outcrop of this unconformity, it cuts as much as down into the Cardenas Basalt. The lowest part of the Nankoweap Formation consists of a basal conglomerate that is composed chiefly of gravel derived from the Cardenas Basalt. The contact between the Tapeats Sandstone and the Cardenas Basalt and rest of the folded and faulted Unkar Group is a prominent angular unconformity.
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These strata unconformably overlie Archean strata of the Superior craton and Proterozoic Richmond Group. The unconformity between the Early Proterozoic Nastapoka Group and the underlying Archean Superior craton lies just inland of Nastapoka arc as defined by the edge of arcuate eastern coastline of Hudson Bay. The unconformity consists of undeformed stromatolite-bearing dolomites overlying either foliated Archean granodiorite or the tilted and eroded strata of the Richmond Gulf Group. A thin, conglomeratic quartz sandstone separates the dolomites from the underlying strata and forms the base of the Nastapoka Group.
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The Ojo Alamo formation is divided into two subunits separated by a large unconformity—a gap in the geologic record. The lower Naashoibito member (sometimes considered part of the Kirtland Formation) was deposited during the Maastrichtian age of the Cretaceous period, specifically between about 69-68 million years ago. It overlies the De-na-zin member of the Kirtland formation, though the two are separated by another large unconformity that spans a period of geologic time equivalent to 73-69 million years ago.Sullivan, R.M., and Lucas, S.G. 2006.
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The Variscan orogeny is expressed as an important unconformity within the Paleozoic sedimentary succession, usually placed above the Lower Westphalian (Bashkirian) and below the Stephanian (Moscovian), but sometimes already below the Upper Westphalian. The tectonic movements therefore happened about 310 million years ago, dated by fossil plants. The Upper Westphalian shows an important unconformity at its base and is made up of conglomerates. The Moscovian is represented by blue- black shales, overlain by the so-called Grey Unit of the Kasimovian (Stephanian B) and the Transitional Layers of the Gzhelian (Stephanian C and Autunian).
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The Toyonishi Group is approximately 300–900 m thick, lies with a disconformity or a locally angular unconformity on the Jurassic Toyora Group, and is overlain with an unconformity by the Early Cretaceous Kanmon Group. It has been divided into the Kiyosue Formation and overlying Yoshimo formations, and exposes in the following three districts: Ohchi-Utsui-Kikugawa, Yoshimo, and Murotsu. The mountainous Ohchi(former Kiyosue) and west Yoshimo coastal areas are type areas of the Kiyosue Formation and the Yoshimo Formation, respectively.Matsumoto, T., 1954, The Cretaceous System in the Japanese Islands.
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The late Cretaceous is absent due to an unconformity. The coal, limestone and shale-laden Tura sandstone, deposited from the Paleocene to the Eocene is 377 meters thick, and lies beneath the middle Eocene Sylhet limestone and late Eocene Kopili shale. An additional unconformity separates Eocene and Oligocene Jennum and Renji sanstone and shale sequences, which are 646 meters in thickness. Lower Bhuban, Middle Bhuban, Upper Bhuban and Boka Bil are ascending units of early Micoense siltstone and sandstone, which give way to the middle Miocene Tipam Sandstone and Girujan Clay.
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The rugged point shows gently sloping beds of red sandstone above vertical beds of greywacke, forming a classic example of Hutton's Unconformity. Siccar Point is notable in the history of geology as a result of a boat trip in 1788 in which geologist James Hutton observed the angular unconformity of the point. He wrote later that the evidence of the rocks provided conclusive proof of the uniformitarian theory of geological development; that is, that the natural laws and processes which operate in the universe have never changed and apply everywhere.
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Subaerial unconformities are used as limiting surfaces that define sequences in sequence stratigraphy. In this context they are synonymous with the terms lowstand unconformity, regressive surface of fluvial erosion as well as fluvial entrenchment surface and incision surface.
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The transition to the Vectis Formation is also present in Swanage but thins out and disappears westward, having an erosive unconformity with the Lower Greensand Group or the Gault in these areas, often with a basal pebble bed.
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The Kukri Peneplain is a near-horizontal and flat unconformity in the Transantarctic Mountains. The peneplain formed by erosion of the granitic and metamorphic basement rocks during the Paleozoic (Silurian to Devonian). Kukri Peneplain dips gently to the west.
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The Great Falls themselves formed on a fall line unconformity in the Great Falls Tectonic Zone.Botkin, Daniel B. Beyond the Stony Mountains: Nature in the American West from Lewis and Clark to Today. New York: Oxford University Press, 2004.
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Erosion returned, forming a third unconformity. The Chinle Formation was then laid down on top of this eroded surface. Increasingly dry climates dominated the Triassic. Therefore, sand in the form of sand dunes invaded and became the Wingate Sandstone.
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Plaque gives brief details of Eparchaen Unconformity The Tirupati hills are situated at the foot of a range of hills known by several names, including 'Seshachala', 'Venkatachala' and 'Balaji'. There are four geological units: :(1) Archaean rocks of the eastern Dharwar Craton (the granites and gneisses) :(2) the Eparchean unconformity (Quartzose sandstones overlying the granite with a distinct unconformity) :(3) Puranas (a general name for Proterozoic sedimentary sequences found in a series of basins deposited on the Indian Shield; including the Cuddapah Basin) Balasubrahmanyan, M.N. 2006. Geology and tectonics of India: an overview, Memoir No.9, International Association for Gondwana Research :(4) Quaternary deposits The Tirumala hills essentially of precambrian period are composed of sedimentary rocks - quartzites and intercalated shales, which are referred to as the Nagari quartzites, which forms part of the Cuddapah Supergroup. It is a subset of the Purana rock succession that rests above the archaean rocks.
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Los Colorados Formation is partly covered by the Cretaceous Cerro Rajado Formation, separated by an unconformity. The formation is known for its fossils of early dinosaurs, including the coelophysoid Zupaysaurus and the "prosauropods" Coloradisaurus, Lessemsaurus, and Riojasaurus.Weishampel et al., 2004, pp.
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It contains abundant fossils near the base. It ranges from 0 to 100 feet thick. The variable thickness is due to an erosional unconformity caused by an ice age at the end of the Ordovician, which lowered global sea level.
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The Chalk Group consists of a sequence of chalky limestones with some interbedded marls. The age of the sequence ranges from Cenomanian through to Campanian, The upper boundary is an unconformity across which rocks of Maastrichtian to Paleocene age are missing.
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Because of progradation later deposits ended up on the lower rise and the abyssal plain. Then large channel-levee complexes developed on the upper rise resulting in an unconformity associated with the Middle Miocene intensification of the Antarctic Circumpolar Current.
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Using geochemical and stratigraphic data from 830 locations across North America they found evidence that the Great Unconformity affected ocean chemistry such that it may have triggered the evolution of Biomineralization, an essential factor of diversification of the Cambrian Explosion.
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Vampire Formation is a formation of delta-front siliciclastics deposited in the early Cambrian. The upper unit is trilobitic Cambrian. Some authors place the underlying Ingta formation at least partially in the Cambrian; in places it overlies the sub-Cambrian unconformity.
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Tirupati Eparchaean Unconformity, a notified National Geo-heritage MonumentGeo-Heritage Sites, Minister of Mines Press release, 09-March-2016national geo-heritage of India, INTACH is a major discontinuity of stratigraphic significance that represents a period of remarkable serenity in the geological history of the earth i.e. sudden changes and discontinuity in the rock layers in earth's crust. It is seen at the steep natural slopes, road scars and ravines in the Tirupati – Tirumala Ghat road in Chittoor district of Andhra Pradesh, India. In 2001, the Geological Survey of India (GSI) declared the unconformity to be one of the 26 "Geological Monuments of India".
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Geological Society of America Bulletin. 117(11–12):1573–1595. Between the three-member Tonto Group (above) and the Shinumo Quartzite, and the rest of the folded and faulted Unkar Group, is a prominent angular unconformity, which is part of the Great Unconformity. Though this surface is typically a plane, differential erosion (also areal erosion) of the tilted strata of the Unkar Group left resistant beds of the Cardenas Basalt and Shinumo Quartzite as ancient hills, called monadnocks, that are up to tall. Thin drapes of Tapeats Sandstone of the Tonto Group now cover most of these ancient monadnocks.
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Eventually, deposition of the Barrow Delta's sediment ceased during the early or middle Valanginian due to the continental break up at the southern margin of the Exmouth Plateau. This followed seafloor spreading at the Gascoyne and Cuvier Abyssal Plains and erosion at the surface of the Exmouth, Dampier and Barrow sub-basins and an unconformity at the top of the early to middle Valanginian. By the middle to late Valanginian and through the Cretaceous major transgression occurred with deposit of the Winning Group atop the Valanginian unconformity. The Winning Group consists of Muderong Shale, Windalia Radiolarite, and Gearle Siltsone.
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The quarry Colemans Quarry, is a limestone quarry at Holwell, near Nunney on the Mendip Hills, Somerset, England. The Colemans Quarry complex comprises four pits separated by three roads (including the A361) The quarry exhibits pale to dark grey Black Rock, Vallis and Clifton Down Groups of Carboniferous Limestone with overlying buff-coloured Jurassic oolitic limestone forming an angular unconformity. The ancient Jurassic erosion surface at the unconformity contains oyster shells and abundant marine borings in the top of the Carboniferous Limestone. There are near-vertical fissures and joints in the limestone with varying amounts of calcite mineralization.
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It flows near the Jauja town into a large alluvial plain. Formation of this region and its lake system is attributed to diverse sedimentary, glacial and tectonic activity. The valley formation is dated to the Late Pliocene and early Pleistocene uplift unconformity.
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This play requires intraformational mudstone seal units to be present, as there is no top-seal for reservoirs subcropping the regional base Permian unconformity in the east of the basin, and Carboniferous strata crop out at the sea bed in the west.
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The formation consists of up to of thinly bedded light brown sandstone. It with a slight angular unconformity on the Sloan Canyon Formation and is overlain unconformably by the Exeter Sandstone.Ziegler et al. 2019 The formation is usually assigned to the Dockum Group.
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Sandy beds may be crossbedded, which is evidence of shallow water origin. The Patuxent is the basal unit of the Coastal Plain sedimentary formations and unconformably overlies the crystalline basement rocks. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard Fall Line.
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The Durroon Basin is south east of the Bass Basin. Late Cretaceous rocks are conglomerate, with sandstones above. From there was a high thermal gradient of 55° per km. Around there was uplift and erosion of 900 m of sediment called Southern Ocean breakup unconformity.
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14 The Tarjados Formation, as the underlying Talampaya Formation, belongs to the Paganzo Group.Tarjados Formation at Fossilworks.org The formation is exposed in the Talampaya National Park of La Rioja Province. The Tarjados Formation is overlain by the Chañares Formation, separated by a regional unconformity.
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Siccar Point is a rocky promontory in the county of Berwickshire on the east coast of Scotland. It is famous in the history of geology for Hutton's Unconformity found in 1788, which James Hutton regarded as conclusive proof of his uniformitarian theory of geological development.
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The base of the Unkar Group is a major unconformity that also forms the base of the Grand Canyon Supergroup. This unconformity is a nonconformity that separates the underlying and deeply eroded crystalline basement, which consists of granites, gneisses, pegmatites, and schists of the Vishnu Basement Rocks, from stratified Proterozoic rocks of the Unkar Group. This contact is a remarkably smooth surface that has a relief of about in the Shinuino 15-minute topographic quadrangle and in both the Bright Angel and Vishnu 15-minute topographic quadrangles. In Hotauta Canyon, and at Granite Narrows, this surface is extremely smooth with a relief of only a few meters.
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The natural geological arch has two distinct physiographical regions – southwest upland and northeast lowland. The Tirupati hills, at the foot of a picturesque range of hills, are known by several names such as 'Seshachala', 'Venkatachala' and 'Balaji'. The geological formations are categorized under four heads namely, the (1) Archeans (the gneisses), (2) the Eparchean unconformity (Quartzose sandstones Overlying the granite with a distinct unconformity), (3) Puranas (formation of Cuddapah group well developed in the valley) and (4) Quaternary deposits. The Tirumala hills essentially of precambrian period are composed of sedimentary rocks – quartzites and intercalated shales, which are given the geological, stratigraphical nomenclature of Nagari quartzites.
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The base of the Bass Formation is a major unconformity that also forms the base of the Grand Canyon Supergroup and the Unkar Group. This unconformity separates the underlying and deeply eroded crystalline basement, which consists of granites, gneisses, pegmatites, and schists of the Vishnu Basement Rocks, from stratified Proterozoic rocks of the Grand Canyon Supergroup. This contact is a remarkably smooth surface that has a relief of about in the Shinumo 15-minute topographic quadrangle and in the Bright Angel and Vishnu 15-minute topographic quadrangles. In Hotauta Canyon, and at Granite Narrows, this surface is extremely smooth with a relief of only a few meters.
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Active stretching and rotation of fault blocks then occurs during the main rift stage is then terminated by the development of the syn-rift unconformity. Syn-rift architectures can be highly variable depending on the ability of the available sediment supply to fill accommodation formed by rotation and subsidence during this stage. Where crustal separation is accomplished, a break-up unconformity commonly marks the boundary to the overlying thermal relaxation of post-rift stage. During the post-rift stage, an early phase with coarse clastic infilling of remnant rift topography often precedes late stage widening of the basin and filling with fine-grained sediments.
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Early geologists had interpreted angular unconformities in terms of Neptunism (holding that rocks had formed from the crystallisation of minerals from ocean waters after the Great Flood) but Hutton wanted to examine such formations himself in support for his theory of Plutonism, in which rocks are formed from volcanic action. Hutton Unconformity at Inchbonny, Jedburgh. A photograph shows the current scene (2003), below Clerk of Eldin's illustration of 1787. On a trip to the Isle of Arran in 1787 he found his first example of an unconformity to the north of Newton Point near Lochranza, but the limited view did not give the information he needed.
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The time between the erosion of the lower unit and deposition of the horizontal sandstone above, is about 1 billion years-(1,000 million years), and is named the Great Unconformity. Besides its occurrence in the Grand Canyon, it is also found west, in the Las Vegas Valley, at Frenchman Mountain. The Zoroaster Granite and other granites, were intruded into the major unit of the Vishnu Schist, the basement paleo unit found in the Inner Gorge region of the Grand Canyon. The neighboring Sierra Ancha range has another occurrence of the Great Unconformity, with a sandstone unit that is an analogue of the Tapeats Sandstone.
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The Belsa Formation is found within the Maestrazgo Basin. Within the stratigraphic sequence it overlies Jurassic rocks in a syn-rift unconformity, and underlies the Alacón Formation. The formation is up to 150 metres thick and is divided into three distinct unconformity bounded units, which are called the Lower, Middle and Upper Blesa Sequences. The Lower Blesa sequence varies greatly in thickness from less than 10 m up to 100 m is divided up into two members, the lower Cabezo Gordo Member, which consists of red clays and the upper Morenillo Member, which consists of limestones and marls, both of these sequences were deposited in a continental setting.
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Then more conglomerate sandstone and mudstone matching the Wangerrip Group up to early Eocene. Quartz sandstone is above this, with marl, mudstone and limestone from Oligocene and Miocene age. There is an unconformity at the Pliocene base. Approximately 4 km of sediment is found in each subbasin.
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Overlying this unit, separated by a small unconformity, is the 'middle rift' unit of Pliocene coarse grained sandstones and conglomerates. Finally there is the modern rift unit of fluvial, glacial, and deltaic sediments. Examining Pliocene and younger sediments reveals sands, argillites, and silts, indicating lacustrine deposition.
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Longpre et al., "Volcanic and geochemical evolution of the Teno Massif, Tenerife, Canary Islands (1. Introduction)", American Geophysical Union, 2009 The flows have subsequently been intruded by several swarms of dykes, many of which form cross-cutting relationships. A particular formation of interest is the Masca Unconformity.
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The Beaufortian Sequence was deposited from the Jurassic to Lower Cretaceous. This sequence of deposition is dominated by shale and consists of syn-rift deposits supplied by local erosion. There are multiple unconformities present throughout this sequence. The most important is the Lower Cretaceous Unconformity (LCU).
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The conglomerates also contain pyrite. These deposits have been mined in the Blind River-Elliot Lake district of Ontario, Canada, and from the gold-bearing Witwatersrand conglomerates of South Africa. Unconformity-type deposits make up about 33% of the World Outside Centrally Planned Economies Areas (WOCA)'s uranium deposits.
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La Meseta Formation lies unconformably on the Cretaceous Lopez de Bertodano Formation. It is an approximately thick sequence of poorly consolidated sandstones and siltstones. The depositional environment was probably coastal, deltaic or estuarine in character. The top of the sequence is an erosional unconformity to Pleistocene glacial gravels.
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The Eparchaean Unconformity of the Tirumala Hills is a major discontinuity of stratigraphic significance that represents an extensive period of erosion and non-deposition. It is seen at the steep natural slopes, road scars and ravines in the Tirumala ghat roads in the Chittoor district of Andhra Pradesh.
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This sequence, which is also ~1000 meters thick begins with an unconformity which lies at the top of the previous sequence. During this time, clastic sediments continue to be deposited, resulting in the shelf prograding further west, while the deep regions of the basin see continued turbidite deposition.
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In a stratigraphic trap, the geometry allowing the accumulation of hydrocarbons is of sedimentary origin and has not undergone any tectonic deformation. Such traps can be found in clinoforms, in a pinching-out sedimentary structure, under an unconformity or in a structure created by the creep of an evaporite.
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Streams eroded the poorly cemented Navajo Sandstone, and water caused the sand to slump. Desert conditions returned briefly, creating the White Throne member, but encroaching seas again beveled the coastline, forming a regional unconformity. Thin beds of clay and silt mark the end of this formation.Harris 1997, p.
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The Triassic contains Xikou, Xiwei, Anren Dakeng Formations followed by a partial unconformity, then Wenbinshan, and Jiaokeng Formation containing conglomerate. The Xikou Formation in Southwest Fujian, consists of a fine grained turbidite. In the areas near Longyan Yongding and Zhangping there are large blocks of oolitic limestone embedded.
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The Lytle Formation consists of white to light gray gravels and conglomerates. It is variable in thickness but is about at the type location. It is separated from the underlying Morrison Formation by a significant regional unconformity. It is overlain by the South Platte Formation or the Glencairn Formation.
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Deposition resumes in the western portion of the Zonguldak basin with the deposition of the Çakraz Formation. The Çakraz spans the upper Permian through the Lower Jurassic. Unconformably overlying the Çakraz is the Inalti Formation. The Inalti was deposited during the upper Jurassic and is truncated by an unconformity.
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See Gradstein et al. (2004) for a detailed version of the geological timescale The Campanian was an age when a worldwide sea level rise covered many coastal areas. The morphology of some of these areas has been preserved: it is an unconformity beneath a cover of marine sedimentary rocks.
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At 12 km point on the Tirupati – Tirumala ghat road, there is a major discontinuity of stratigraphic significance that represents a period of remarkable serenity in the geological history of the Earth. This is referred to as Eparchaean Unconformity. This unconformity separates the Proterozoic Nagari Quartzite and the Archean granite representing a time gap of 800 Ma. In 2001, the Geological Survey of India (GSI) declared the Eparchaean Unconfirmity to be one of the 26 "Geological Monuments of India". Silathoranam (natural arch) at Tirumala Hills, Tirupati, Andhra Pradesh Silathoranam, a natural arch and a distinctive geological feature, is located in the Tirumala Hills at a distance of 1 km from Tirumala Venkateswara Temple.
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The contact between the Tapeats Sandstone and Bass Formation and the rest of the folded and faulted Unkar Group is a prominent angular unconformity, which is part of the Great Unconformity. The differential erosion of the Unkar Group left resistant beds of the Cardenas Basalt and Shinumo Quartzite as topographic highs, (today seen as ancient & weathered monadnocks), that are now buried by sandstones, shales, and conglomerates of the Tapeats Sandstone. These monadnocks served locally as sources of coarse-grained sediments during the marine transgression that deposited the Tapeats Sandstone and other members of the Tonto Group. The contact between the Bass Formation and the Tapeats Sandstone forms part of a relative flat surface that lies between the monadnocks.
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Around the end of the Cretaceous and the start of the Cenozoic, the sedimentary rocks in the Chad Basin were folded into anticlines and synclines. Erosion created an unconformity with younger rocks. Terrestrial sediments built up in the Paleocene Kerri Kerri Formation, followed by Pliocene lake sediments of the Chad Formation.
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At intermediate levels sandstone is common. Some parts of the paleic surface in Varanger Peninsula are a re-exposed unconformity that underlie sedimentary rock of Vendian (Late Neoproterozoic) age. The paleic surface might have been uplifted as much as 200–250 meters since middle Pliocene times.Fjellanger, J. & Sørbel, L. (2007).
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The Ucayali Peneplain is a large near-flat erosion surface, a peneplain, located in the Amazon basin. The Ucayali Peneplain is largely buried by sediments forming an unconformity. Its origin has been dated to the Miocene epoch. The Peneplain was first described in 1948 in the Contamana region of Peru.
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Carboniferous Limestone exposed at Ogmore-by-Sea, Wales. Carboniferous/Jurassic unconformity. Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 and 325 million years ago.
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An angular unconformity separates weathered basement rock from the Merkys Formation fanglomerates, formed in the Neoproterozoic. Salica Formation arkose and siltstone overlies these units, overlain in the east by the Kieva Formation with siltstone, clay and sandstone. Sedimentary rocks up to 2.3 kilometers thick define the entire Phanerozoic rock record.
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Conglomerates are normally present at the base of sequences laid down during marine transgressions above an unconformity, and are known as basal conglomerates. They represent the position of the shoreline at a particular time and are diachronous.Seibold, E. & Berger, W.H. 1996. The Sea Floor: an introduction to Marine Geology, Springer.
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The Nam Phong Formation, which correlates to the Indosinian III Unconformity, is a geological formation in Thailand. It underlies the Khorat Group. It consists of resistant, red-brown micaceous sandstones, conglomerates, siltstones and mudstones of mainly fluvial origin. The sandstones are medium to very fine-grained and are usually calcareous.
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These are found near Foz do Douro, and Miranda do Douro. Above this are schists or shales with beds of turbidites or limestone interleaved. The stratigraphic sequence can be observed south west of Salamanca in the Tamames Syncline, and in the Montes de Toledo. These are followed by an unconformity.
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Geological Survey of Canada. Retrieved March 2017. The CSBC and the Yellowknife greenstone belt are separated by a distinct unconformity that is laterally continuous over hundreds of kilometres. The Yellowknife Supergroup has been exposed to major metamorphism around 2605 Ma resulting in a range of greenschist to lower amphibolite facies.
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The Consuelo Formation was described by Bermúdez in 1950 based on a section of marls in the Consuelo El Tejar quarry in La Habana Province.Gutiérrez Domech, 1969, p.32 The formation overlies the Príncipe and Capdevila Formations with an unconformity,Gutiérrez Domech, 1969, p.33 and is overlain by the Tinguaro Formation.
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When the two overriding plates collide and the ocean basin is closed, sedimentation ceases. Sinking of the oceanic plate drag down the welded crust to form a basin that allows continued sedimentation. After the oceanic plate completely detaches from the crust above, isostatic rebound occurs, leaving a significant unconformity in the sedimentary sections.
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The uplift and erosion which followed is evidenced by an unconformity across Africa and South America. It is related to the breakup of Gondwanaland. Following the Gondwanide orogeny southwestern Gondwana entered a period of extensional tectonics and crustal thinning leading to formation of various rift basins (e.g. Cuyo Basin) in the Triassic.
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The formation was first named by C.L. Herrick in 1900 for exposures in the Sandia Mountains of New Mexico. Herrick included the entire sequence of clastic beds resting on the Great Unconformity. Gordon identified the clastic beds between the Kelly Limestone and Madera Limestone in the Magdalena Mountains as Sandia Formation.Duchene 1974, p.
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The Kozlu is composed of successional conglomerate, sand, silt, mud, and coal deposits. The Karadon Formation conformably overlies the Kozlu. The Karadon is lithologically similar to the Kozlu Formation, but contains less coal seams. An angular unconformity spans the top of the Karadon formation and ranges from 46.5 Ma–194 Ma in duration.
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The Kilimli is composed of sandstone and carbonaceous sandstone. The Kilimli is unconformably overlain by the sandy limestone of the Cemaller Formation. The unconformity lasts at least 6.5 Ma and the Zonguldak basin experiences continuous deposition from the Turonian – Campanian. The Cemaller is overlain by the siltstone and limestone of the Baþköy Formation.
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Rocky Mountain Geology vol. 38, no. 1, p. 45-71. In 2002 the Dawson Arkose was included as part of a larger unconformity-bounded unit named the D1 Sequence, in order to facilitate basin-wide studies and avoid confusion arising from the lateral and vertical facies changes that occur within the Denver Basin.
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GSI's commemoration document, published on the occasion of the 150 years anniversary celebration, provides an insight into the formation of the subcontinent, the orogeny, the paleoenvironment and the exotic collection of paleo-flora and fauna. The details provided for the Eparchaean Unconformity monument indicate that this feature forms the boundary surface between Proterozoic Nagari Quartzites and Archaean granite. The time gap between the formation of the two units is at least 500 Ma. At this location, the boundary is between sedimentary rocks of the Cudappah Supergroup, 1600 million years in age, and Archaean rocks comprising granites, gneisses and dolerite dykes that are more than 2100 million years old. This unconformity gives an indication of the enormous time gap in the creation of the earth's crust.
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Available here. As the oil field is in the center of a large flat alluvial floodplain, there is no surface expression of any anticlinal structure capable of holding oil. Under the surface alluvium, a series of relatively impermeable sedimentary units cap the petroleum-bearing formation. On top are the Pleistocene San Pedro and Pleistocene-upper Pliocene Santa Barbara formations; under that the Pico Sands, of Pliocene age, which contain areas of tar sands; under that, separated by an unconformity, the Monterey Formation, of Miocene age, which also contains tar sands (the Vaca Tar Sand); under that, again separated by an unconformity, the relatively impermeable Conejo-Topanga Formation, which caps the faulted anticlinal structure containing medium-grade oil about below ground surface.
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Cross-cutting relationships can also be used in conjunction with radiometric age dating to effect an age bracket for geological materials that cannot be directly dated by radiometric techniques. For example, if a layer of sediment containing a fossil of interest is bounded on the top and bottom by unconformities, where the lower unconformity truncates dike A and the upper unconformity truncates dike B (which penetrates the layer in question), this method can be used. A radiometric age date from crystals in dike A will give the maximum age date for the layer in question and likewise, crystals from dike B will give us the minimum age date. This provides an age bracket, or range of possible ages, for the layer in question.
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An angular unconformity separates the overlying Hassaouna sandstones from lower Precambrian rocks. These sandstones are inferred to be Cambrian rocks, formed at the beginning of the Paleozoic. In some cases, purple and blue Murizidie series rocks intercalate the sandstones. Orogeny related sedimentation continued through the Ordovician, until a period of tectonic calm in the Silurian.
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The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion during the formation of the Great Unconformity and prior to deposition of the Tapeats Sandstone.Dehler, CM, SM Porter, and JM Timmons (2012) The Neoproterozoic Earth system revealed from the Chuar Group of Grand Canyon., in JM Timmons and KE Karlstrom, eds., pp.
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These sediments are non-metamorphic or only weakly metamorphosed, whereas the sediments below the unconformity fully experienced the Variscan metamorphism. The far-reaching effects of the Variscan orogeny influenced the pyrenean domain in many ways. Of prime importance were the compressional stresses that folded the Paleozoic sediments. Several fold generations developed, sometimes superimposing each other.
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The Frenchman Formation consists of olive- green to brown, fine- to coarse-grained, cross-bedded sandstone with interbedded claystone bands and minor beds and lenses of intraformational clay-clast conglomerate. A conglomerate layer with well-rounded quartzite pebbles is present above the basal unconformity in some areas.Glass, D.J., editor, 1997. Lexicon of Canadian Stratigraphy, vol.
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2013 aerial photo In the late Eocene to early Oligocene, approximately 34 million years ago, the area was a lake environment with redwood trees. The basement is the Proterozoic aged Pikes Peak Granite. There is an unconformity from the Pikes Peak Granite to the next unit, the Wall Mountain tuff.Foos, A. & Hannibal, J. (1999).
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Southington's west ridge is rich with many geological formations. This includes North Hamlin Brook, Roaring Brook, and Soltys Pond. Soltys Pond was named after Alexander Soltys, who settled in the area in 1713. The most well-known geological formation in the area is one of several in the world known as the Great Unconformity.
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The Torridonian Supergroup is of Neoproterozoic age and consists mainly of sandstone with a maximum preserved thickness of over 8 km. It is divided into three groups, the Stoer, Sleat and Torridon groups. The unconformity at the base of this unit is highly irregular, showing that it was deposited on an eroded land surface.
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This event possibly caused the drowning of sedimentary sources. The balance of sedimentary influx and organic production influenced the establishment of anoxic conditions. Siliciclastic deposits, which are dominated by calciferous organic-rich black shales, were deposited above the unconformity of the top of the Crato Formation. These deposits mark the base of the Ipubi Formation.
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In these exposures, Dox red beds and a dark gray basaltic sill, dip 8 to 10 degrees to the east. They are covered by nearly horizontal Tapeats Sandstone. The surface of this angular unconformity is quite irregular as differential erosion of the resistant basalt sill formed monadnocks that have been buried by Tapeats Sandstone.
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The shortest way up is a straight line from the parking area at Boguillie at grid ref 973483. The hill has a remarkable variety of geology. On its north-western slopes is the famous Hutton's Unconformity in the Dalradian metasediments. On the north-east shore can be found Carboniferous limestone and Permian desert deposits.
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A second unconformity occurred after the Black Mountain Sandstone was uplifted and eroded at the end of the early Silurian. This was called the Quidongan Deformation. The Canberra formation was deposited in shallow water with limestone, and shale forming. There were some small volcanic activities at this stage with dacite and ashstone layers included.
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Cather et al. 2002 The formation is informally divided into a lower well-cemented cliff-forming member and an upper poorly cemented member. The formation lies with angular unconformity on the Blackshare Formation. It is distinguished from the coeval Ancha Formation in containing mostly volcanic clasts, while the Ancha Formation is rich in granite clasts.
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Blå Jungfrun, an inselberg and island formed in connection to the peneplain. In northwestern Finland the Ostrobothnian Plain is a continuation of the peneplain. To the east the Sub-Cambrian peneplain continues as an unconformity beneath the East European Platform. On a grand-scale the peneplain is not completely flat as it has been deformed.
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Further south and west, the formation transitions to lighter-colored sandstone. Maximum thickness is . A characteristic feature of the sandstone is the presence of muscovite. The base of the formation is an angular unconformity with much older beds of Jurassic to Cretaceous age, while the upper contact is an erosional disconformity with the Abiquiu Formation.
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20: 91–116. In 1973, the current definition of the Unkar Group developed when the Nankoweap Formation, which had been earlier added to the Unkar Group was formally removed from it and the unconformity that separates the Nankoweap Formation from the Unkar Group - was recognized.The Development of Geological Studies in the Grand Canyon. Tyrona, Miscellaneous Publications no. 17.
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The type section is in the Wernecke Mtns; it corps out also in and to the S/SW of the Rochardson Moutnars. It possibly corresponds to the Sekwi Fm in the Macxkenzie mtns. Lowermost of the Palaeozoic strata west of the Richardson Mountains, angular unconformity at base, overlying various Precambrian strata. Silty limestones and massive dolomites.
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At intermediate levels sandstone is common. Some parts of the paleic surface in Varanger Peninsula are a re-exposed unconformity that underlie sedimentary rock of Vendian (Late Neoproterozoic) age. The paleic surface might have been uplifted as much as 200-250 meters since middle Pliocene times. Landforms resulting from Quaternary periglaciation are recurrent across the peninsula.
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The Late Cimmerian orogeny occurred as a significant tectonic event in Iran in Late Jurassic–Early Cretaceous times. This event is represented by folding, facies changes in sedimentary environments, angular unconformity, magmatism, and metamorphism (e.g., Alborz, Sanandaj–Sirjan, and Central Iran). The Jurassic granite of Kolah Ghazi, Shir Kuh, and Shah Kuh was made during this orogenic phase.
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Although the field today is in the deepest part of the basin, an unconformity at the base of the Pierre Shale shows that the field is on an early paleohigh active in the Middle Cretaceous.R.J. Weimer and S.A. Sonnenberg, “Wattenberg field, paleostructure- stratigraphic trap, Denver Basin, Colorado,” Oil & Gas Journal, 22 Mar. 1982, p.204-210.
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The eroded units included the Mishrif Member and most of the Rumaila Member. This caused the Aruma unconformity to form. Because of the impact of the regional tectonic events during this time hydrocarbon traps started to form. Burial stage resumed and deposited the Aruma Formation at the end of the Campanian until the end of the Middle Eocene.
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These sediments became the fossil-rich limestones, sandstones, and shales of the gray-colored Honaker Trail Formation. Outcrops of the Honaker Trail can be seen near the bottom of deep canyons in the park, most notably along the Colorado River. A period of erosion then ensued, creating a break in the geologic record called an unconformity.
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The village lies above the Mells River in the Mendip Hills. Vallis Vale is a biological and geological Site of Special Scientific Interest which includes an ancient woodland and exposes some of Britain's most classic rock outcrops, exhibiting several of the most easily demonstrated examples of angular unconformity available.English Nature citation sheet for Vallis Vale . Retrieved 10 August 2006.
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Four depositional sequences have been recognised in the Bahariya Formation in the Bahariya depression, separated by three sub-aerial unconformities. The formation was deposited during a period of relative rise in sea level, with each unconformity representing a relative fall in sea level. Each of the individual sequences contains sediments deposited under fluvial, shoreline and shallow marine conditions.
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The mountain ranges were reduced to hills, and in some places, the whole of the supergroup were removed entirely, exposing the basement rocks below. Any rocks that were deposited on top of the Grand Canyon Supergroup in the Precambrian were completely removed. This created a major unconformity that represents 460 million years of lost geologic history in the area.
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The Black Mingo Group is a geologic group in South Carolina composed of dark grey to black clays, shales, laminated sandy shales, and yellow-red sands. The group's name comes from Black Mingo Creek where outcrops of the group are exposed. The bottom boundary is an unconformity with Cretaceous deposits. It preserves fossils dating back to the Paleogene period.
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Organic-rich shale overlies a major unconformity in the area, acting as the source rock for hydrocarbons. Plate rotation produced the Brooks Range with a plate collision visible at the surface in the Kobuk River. Paleozoic and Mesozoic rocks separated from the descending slab, leaving mineral deposits in the Brook Range related to older rock units.
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Black Eagle Falls is the first in a series of five waterfalls which constitute the Great Falls of the Missouri River in the state of Montana in the United States. Before being dammed, water dropped over the falls.Cutright and Johnsgard, p. 26. Black Eagle Falls formed on a fall line unconformity in the Great Falls Tectonic Zone.
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Within the northwest part of New Siberia Island, these sediments grade into clays that contain fragments of marine bivalves. Directly overlying the Eocene sediments and another erosional unconformity are sands of Oligocene and Early Miocene age. They contain thin beds of silt, mud, clay, and pebbles. These sands contain fossil plants and lagoonal, swamp, and lacustrine diatoms.
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It is above sea level and southeast of Wilkes-Barre's Public Square. An unconformity lies between the Catskill Formation and the Spechty Kopf Formation. The sandstone in the latter formation are mostly cross-bedded, although some areas have planar bedding. The Llewellyn Formation, containing conglomerate and sandstone is found in the Spring Run and Sugar Notch Run sub-watersheds.
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The site employs over 250 people and produces 7.5 million tonnes of limestone annually which is carried directly from the quarry by Mendip Rail. A Geodiversity audit of the site recorded pale to dark grey well bedded Carboniferous Limestone dipping consistently southwards with a small area of overlying horizontally bedded buff-coloured Jurassic oolitic limestone forming an angular unconformity.
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Relative age dating of the Mauch Chunk places it in the late Mississippian epoch, with some of the top layers in the early Pennsylvanian epoch, being deposited between 345 and 320(±3) million years ago. It rests conformably atop many formations. Its upper contact is complex. In certain areas, the contact is conformable in others, there is an unconformity.
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The formation consists mostly of black to gray shale and minor limestone.Gordon 1907 It rests on a regional unconformity, so that the underlying formation may be the Fusselman Formation,Stevenson 1945 the Sly Gap Formation, or the Onate Formation. It underlies the Lake Valley Limestone, Caballero Formation, Escabrosa Limestone, or other Mississippian formations. Total thickness is about .
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In the South Texas subsurface, the age equivalent unit to the Langtry Member is more calcareous than the underlying Upper Eagle Ford rocks, making them difficult to distinguish from the limestones of the overlying Austin Chalk, although an unconformity is found between the Eagle Ford and the Austin Chalk in both South Texas and East Texas.
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0.5 metre at Jet Wyke. They reside within the upper part of the Amaltheus margaritatus faunal zone and are collectively referred to as the Penny Nab Member, after a headland c.150 metres east of Staithes Harbour. An unconformity marks transition to the overlying Pleuroceras spinatum zone which covers the more ferruginous upper 6 metres of the formation.
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In the northeast Grand Canyon, the Tapeats is still the defining cliff unit at the Great Unconformity between the paleozoic Tapeats Sandstone and the basement geology below. However, the entire east of the Kaibab Plateau is an uplifted side of the East Kaibab Monocline.Chronic, Halka. Roadside Geology of Arizona, from Section: "Grand Canyon National Park", pp. 279-287.
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The unconformity, believed to have been formed by subaerial erosion, was the surface of a peneplain at the time of deposition of the Dala sandstone. The peneplain landscape formed after protracted periods of erosion. Sedimentation of the Dala sandstone happened between 1650 and 1200 million years ago. The maximum thickness of the sediments at Dalarna is 800 m.
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Evidence of fluvial activity was observed early on in the mission at the Shaler outcrop (first observed on Sol 120, investigated extensively between Sols 309-324). Observations made by the rover Curiosity at the Pahrump Hills strongly support the lake hypothesis: sedimentary facies including sub mm- scale horizontally-laminated mudstones, with interbedded fluvial crossbeds are representative of sediments which accumulate in lakes, or on the margins of lakes which grow and contract in response to lake-level. These lake-bed mudstones are referred to as the Murray Formation, and form a significant amount of the Mount Sharp group. The Siccar Point group (named after the famous unconformity at Siccar Point) overlies the Mount Sharp group, and the two units are separated by a major unconformity which dips toward the North.
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Journal of the Geological Society, 153: 451-466. The age and stratigraphic equivalents of the Hoy sandstone sequence are a matter of continuing debate. Traditionally the presence of an unconformity at the base of the lavas beneath these sandstones on southwestern Hoy has been interpreted to mark a major time break.Mykura, W. (with contributions by Flinn, D, & May, F.) 1976.
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The middle of this member contains numerous thin discontinuous beds of chalky- white chert. The lower part of the Middle Member is purplish red, which grades upward to a creamy mottled and streaked red. This member is resistant to erosion and characteristically forms cliffs. This member forms small hills within the Great Unconformity on either side of the Chuar syncline.
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Stratigraphically, an unconformity occurs around 260 Ma, indicating terrestrial erosion conditions. The full geochronology of the Mesozoic is unknown in Nebraska because Triassic and Jurassic rocks are not preserved. Only Cretaceous formations exist, visible primarily in the eastern part of the state. The Dakota Formation is the oldest Cretaceous formation, deposited 100 Ma and containing a mix of sandstones, siltstones, mudstone and shale.
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Secondary red beds are characterized by irregular color zonation, often related to sub-unconformity weathering profiles. The color boundaries may cross-cut lithological contacts and show more intense reddening adjacent to unconformities. Johnson et al. (1997) have also showed how secondary reddening phases might be superimposed on earlier formed primary red beds in the Carboniferous of the southern North Sea.
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Maungdaw district. The Indo-Burman Range is a sedimentary belt mainly consisted of Cenozoic flysch sediments and a core of Mesozoic ophiolites dated back to late Jurassic overlain on a thick Mesozoic sequence. All the above unconformity lies on a metamorphic basement dated back to pre-Triassic. The core Mesozoic ophiolites consists of serpentinite peridotites, pillow basalts and red cherts etc.
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The Bluestone Formation is a geologic formation in West Virginia. It is the youngest unit of the Upper Mississippian-age Mauch Chunk Group. A pronounced unconformity separates the upper boundary of the Bluestone Formation from sandstones of the overlying Pennsylvanian-age Pocahontas Formation. Two formally named subunits of the Bluestone Formation, the Bramwell and Pride Shale Members, are quite fossiliferous.
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Sheep Rock is an overlook of Hells Canyon in the Payette National Forest about 45 miles northwest of Council, Idaho. It was designated a National Natural Landmark in 1976. The formation consists of two contrasting series of layers from the Columbia River Basalt Group. The layers are separated by an unconformity and provide an unobstructed view of this type of geologic phenomenon.
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The Everts formation (70 mya) is dominated by sandstone and has coal seams from plant debris that collected in swampy areas. There are no rocks on Mt. Everts from 65 to 2.1 million years ago. The absence of rocks is called an unconformity. During this period few or no rocks were deposited, and erosion carried away any sediments that were deposited.
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There is an unconformity where the Karoo rocks of the basin overlie much older rocks. The southern flank of the basin is underlain by Waterberg Group rocks, which form between two-thirds and three-fourths of the basin floor. Mafic rocks of the Limpopo Belt underlie the basin floor in the northeast. The Bushveld Complex underlies the basin in the southeast.
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The Cambrian to lower Ordovician rocks consist of two groups, the Ardvreck Group and the Durness Group. The Ardvreck Group lies above an angular unconformity over various parts of the Torridon Group and locally over the Lewisian. It is a sequence of mainly quartz arenites. The lowermost part of the Eriboll Formation, the Basal Quartzite Member, is often pebbly at its base.
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Farellones Formation () is a geological formation of Miocene age in the Andes of Central Chile up almost entirely of volcanic and volcaniclastic rocks. At some location reaches thicknesses in excess of . It overlies the Oligo–Miocene Abanico Formation across a diachronous unconformity. The best exposure of the formation is said to be at the ski resort of Farellones east of Santiago.
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The Bajada Colorada Formation, first defined by Roll in 1939, pertains to the Mendoza Group.Moyano Bohórquez, 2004 It overlies the Quintuco and Picún Leufú Formations and is overlain by the Agrio Formation. The contact with the Agrio Formation is discordant and the unconformity has been dated to 134 Ma.Leanza, 2005, p.151 The formation is laterally equivalent with the Mulichinco Formation.
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The Neshoba Sand Member was named for Neshoba Co., Mississippi and is a non-fossiliferous sand. It was considered part of the Winona Formation, but was separated out due to its low glauconite concentration and the presence of an unconformity. The sand grains grow steadily coarser from top to bottom, and is thought to represent a marine regression depositional environment.
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The productive section in the field is associated with a regional unconformity between the Oligocene Icotea Formation and the older Eocene sandstones. Shales and other tight formations in the Icotea Formation provide the trap preventing vertical migration. On the east side of the field a large strike-slip fault provides additional trapping of oil, preventing it from moving laterally to the east.
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Paleocurrents confirm deposition by stream flow from the Ortiz Mountains to the east. The total thickness is over . The formation is divided into four informal members, described as a sandstone facies, a conglomeratic sandstone facies, a conglomerate facies, and a muddy sandstone facies. The formation interfingers with the underlying Tanos Formation and is overlain with angular unconformity by the Tuerto Formation.
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Interlayered with these sandy limestones are oyster beds, iron oolite and gypsum layers; they contain ammonites like Pleydellia aalensis and Leioceras opalinum. The sequence ends with an erosional unconformity. In the southern part of the Aquitanian basin, the evaporite deposition (including layers of anhydrite) begun in the Triassic carries on right through the Lias; it reaches a thickness of up to 500 m.
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Since the onset of the Albian, strong halokinetic movements affect the southern Aquitaine Basin and in turn profoundly influence sedimentation patterns. As a result, breccias, thick conglomerates, and turbidites are shed. In the Parentis Basin, a distinct unconformity develops. At the same time, the sediments on the Aquitaine Plateau farther north are folded into gentle wavetrains following the Hercynian strike (northwest- southeast).
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The Bullhead Group overlies a major regional unconformity caused by pre-Bullhead erosion. It rests unconformably on the Fernie Formation, the Nikanassin Formation, the Minnes Group or the Kootenay Group, depending on the location and the extent of the erosion. It is overlain conformably by the glauconitic sandstones and marine shales at the base of the Fort St. John Group.
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The Baguio Mining District consists of Late Cretaceous ophiolite basement rocks. These are overlain by Eocene back arc tholeiitic Pugo Metavolcanics. These grade into the Dalupirip Schist, which is separated from the Early Oligocene-Early Miocene sedimentary Zigzag Formation by an unconformity. The Zigzag is composed of deep depositional environment interbedded green sandstones, red siltstones, oligomicitc conglomerates, and minor limestone units.
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Hutton wanted to examine such formations himself to see "particular marks" of the relationship between the rock layers. On the 1787 trip to the Isle of Arran he found his first example of Hutton's Unconformity to the north of Newton Point near Lochranza, but the limited view meant that the condition of the underlying strata was not clear enough for him, and he incorrectly thought that the strata were conformable at a depth below the exposed outcrop. Later in 1787 Hutton noted what is now known as the Hutton or "Great" Unconformity at Inchbonny, Jedburgh, in layers of sedimentary rock. As shown in the illustrations to the right, layers of greywacke in the lower layers of the cliff face are tilted almost vertically, and above an intervening layer of conglomerate lie horizontal layers of Old Red Sandstone.
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This cross-section illustrates how the reactivation of the Sabine Uplift in the East developed the Woodbine/Eagle Ford Unconformity that is present in the subsurface of Far East Texas In the Cretaceous after the Woodbine and Eagle Ford formations were deposited, the Sabine Uplift started to become elevated again due to its reactivation ~88 mya. A decrease in the effective elastic plate thicknesses caused the basin to subside as the uplift became increasingly elevated. As a result, an estimated 150 m of uplift over the Sabine region caused the eastern parts of the Woodbine and Eagle Ford formations to have a subaerial exposure, which eventually resulted in their easterly erosion. Deposition of the Austin Chalk after this erosional occurrence caused a sealing of the East Texas petroleum reservoir and the creation of a middle Cretaceous unconformity.
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British Regional Geology: Orkney and Shetland, Institute of Geological Sciences, Natural Environment Council, 149pp. More recent studies have suggested that this unconformity is of only local significance as a hiatus of this age has not been recognised elsewhere in the Orcadian Basin sequence.Underhill, J.R. & Brodie, J.A. 1993. Structural geology of the Easter Ross Peninsula, Scotland: Implications for movement on the Great Glen Fault Zone.
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Chapman's Peak Drive. The pass is built on top of a layer of granite, cut into the softer sedimentary rocks above. The top of Chapman's Peak consists of flat, sedimentary rocks related to those that form Table Mountain. The base of the mountain, however, consists of Cape Granite and the two formations meet at a geological unconformity that is world-famous amongst earth scientists.
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Mesozoic rocks from 251 to 66 million years ago are largely absent in Guinea-Bissau. In the west, there is an unconformity between Paleozoic sediments and Cenozoic marine sediments, which are cut by mafic dykes. In the past 2.5 million years of the Quaternary, Guinea-Bissau's surficial geology and geomorphology have changed considerably, with the formation of new terraces and duricrust, as well as frequent marine transgressions.
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The 600 Ma Precambrian rocks at Hallet cove are separated from the 270 Ma Permian deposits by an unconformity. If there were periods of deposition between the two periods, erosion has removed all trace. The formation of Pangaea resulted in extensive glaciation over much of Australia during the Carboniferous and Permian. It is believed that by 270 Ma Australia was part of a supercontinent called Gondwanaland.
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The 200 m thick Estana Formation is made up of limestones and calcareous shales. Its end–Ordovician limestones contain a benthic fauna (brachiopods, bryozoans, cystoids) as well as conodonts. The succession ends with the badly layered Ansobell Formation (20 to 300 m), dark schists that bear microconglomerates indicating a glaciomarine depositional environment. The Ansobell Formation can develop an unconformity and sometimes follows directly upon the Cava Formation.
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During Middle Ordovician to Late Silurian, these two previously drifted apart blocks were collided with each other again, forming the large South China Block. This event is referred as the South China Caledonian orogeny which probably took place in 430–400 Ma. There exhibited an angular unconformity in high angles between the Silurian rocks and the Carboniferous rocks in which the Devonian units were missing.
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The forearc basin depositional environment is characterized by a low geo-thermal gradient. This relatively cool environment, along with the shallow nature of the seafloor as well as the depositional beds provide a welcoming setting for the creation of hydrocarbons. The coal beds above the second unconformity would be the source of these hydrocarbons, but this area has only just begun being explored for oil/natural gas.
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A major Permo-Triassic deformation event in the Karatau Range occurs north of Muruntau as well. This event is synchronous with the major unconformity above. The main mechanism of this event is the giant Karatau Fault, which has right-lateral displacement of and related steeply-plunging Z-shaped folds. Outcrops of the basement throughout the region are elongate in the direction of strike-slip faulting, northwest.
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In the Triassic, at the beginning of the Mesozoic, a meteorite struck McKenzie County, rearranging older sediments. Some salt and gypsum remains from the time period, indicative of the vast deserts that covered Pangea at the time. An unconformity wipes out 45 million years of the early Jurassic before the beginning of the Zuni Sequence. North Dakota was a low forested landscape experiencing ongoing erosion.
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The first sequence was deposited in the Jurassic during the rifting which caused the initial formation of the basin. This Jurassic formation is called the Girón Formation which consists of siltstones and rhyolitic tuffs. During this period, the basin also experienced granitic plutonism along its western margins. The Jurassic-Cretaceous angular unconformity, separating the first and second sequence, is representative of the post-rift boundary.
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The Lohan Cura Formation is a geologic formation with outcrops in the Argentine provinces of Río Negro, Neuquén, and Mendoza. It is the second oldest Cretaceous terrestrial formation in the Neuquén Basin. The Lohan Cura Formation unconformably overlies the terrestrial La Amarga Formation. In some places it also overlies the older marine Agrio and Bajada Colorada Formations of the Mendoza Group through the same Middle Miranican unconformity.
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Within the Jaisalmer petroleum has been explored by various oil companies including Focus Energy, Oil & Natural Gas Corporation (ONGC) and Oil India Limited in the Lower Goru, Pariwar formations of Jaisalmer sub Basin. Clastic sandstones serve as the reservoirs. these include the Baisakhi-Bedesir, Pariwar, Goru, Sanu and Khuiala formations. Traps in this area are restricted to fault related closures and unconformity related traps.
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The Ross Sea-wide major unconformity RSU-6 has been proposed to mark a global climate event and the first appearance of the Antarctic Ice Sheet in the Oligocene. During 2018, Expedition 374 of the International Ocean Discovery Program (IODP), the latest successor to the DSDP, drilled additional holes (U1521-1525) in the central Ross Sea for determining Neogene and Quaternary ice sheet history.
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Sawn sample of the Génis porphyroid showing a dextral shear sense. Below a pronounced angular unconformity one encounters the Génis porphyroid. This rock represents alkaline, rhyolitic ignimbrites (metaignimbrites) of lower Ordovician age (Tremadocian). Its mineralogy is composed of phenocrysts of quartz, alkali feldspar and plagioclase (albite) and a very fine-grained matrix (grain-size 5 μ) made of quartz, feldspars, sericite and rare chlorite.
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An unconformity cutting across the Marañón fold and thrust belt show the Incaic Phase ended no later than 33 million years ago in the earliest Oligocene. Topographic map of the Andes by the NASA. The southern and northern ends of the Andes are not shown. The Bolivian Orocline is visible as a bend in the coastline and the Andes lower half of the map.
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The Cedar Mountain Formation is sandwiched between the Morrison Formation below and the Naturita Formation and Mancos Shale above. The youngest date for Morrison just below the Cedar Mountain Formation is 148.1 ± 0.5 Ma . or lower Tithonian. Typically, the Jurassic-Cretaceous boundary in western North America is marked by an unconformity of variable length, and typically signifies 10-49 million years of missing geologic time.
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Above the unconformity can be found reddish sandstone, shale and conglomerate of Tremadocian age up to 1 km thick. An Arenigian age quartzite formation is equivalent to the Amorican Quartzite. Then there is black shale or slate matching the Luarca Slate of Llanvirn to Llandeilo Age. On top of this is the Botella or Cantera Quartzite, 0.1 km thick of Llandeilian to Caradocian Age.
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The geological importance of the Caballo Mountains lies in the variety and scope of their exposed rocks. Geologists can assess exposed rock formations in several ways. Relative dating compares the formation's bedding location in comparison with other formations nearby. This allows not only the identification of the older and younger formations, but conclusions about unusual local conditions, such as folding, a fault displacement, or an unconformity.
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Brightly colored oxidized muds were then deposited, forming the Organ Rock Shale. Coastal sand dunes and marine sand bars once again became dominant, creating the White Rim Sandstone. Rock formations in the Needles district A second unconformity was created after the Permian sea retreated. Flood plains on an expansive lowland covered the eroded surface and mud built up in tidal flats, creating the Moenkopi Formation.
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Typically, these units are one to two kilometers thick. The Kurama Unit has volcanic rocks from the Ordovician, Silurian turbidites and andesite flows. An angular unconformity separates these rocks from a Devonian molasse unit, striking to the northeast with layers of andesite and tuff and overlain by a Devonian to Carboniferous carbonate unit. A volcanic unit caps the sequence, extending into Early Triassic age.
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The park's geologic record preserves three different groups of rock and sediment. The oldest rocks are Early to Middle Proterozoic gneiss and schist, including the Ute Canyon Stock. Overlying these, and separated by an angular unconformity, are mostly horizontally bedded Mesozoic sedimentary rocks, including the cliff-forming Wingate Sandstone. Overlying these are various types of Quaternary unconsolidated deposits such as alluvium, colluvium, and dunes.
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Some authors believe that there was an unconformity during the Brioverian succession, as there are phtanite stones in the upper parts believed to be eroded from the lower parts, but this is still inconclusive. Cadomian magmatism has been dated in the intrusions and volcanics as . Foliated quartz diorite occur at Baie de St Brieuc, at Coutances, La Hague, Guernsey, Alderney and Sark. These are only roughly dated .
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Winnock, E., and Pontalier, Y., 1970, Lacq Gas Field, France, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, pp. 370 and 386. The field is 16 km long and 10 km wide with oil produced beneath a Tertiary unconformity at 700 m and gas, with high hydrogen sulfide content, beneath a pre-Cretaceous unconformity at about 4000 m.Winnock, E., and Pontalier, Y., 1970, Lacq Gas Field, France, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, pp. 370 and 386. The anticline was identified with two exploration geophysics electric lines in 1943 and a magnetotelluric survey in 1943, a gravimetric survey in 1944 and a reflection seismology survey in 1947, which led to the Lacq No. 1 well in 1949.Winnock, E., and Pontalier, Y., 1970, Lacq Gas Field, France, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, p. 374.
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The upper contact of the Vishnu Basement Rocks is a major unconformity between it and either the Tonto Group or Unkar Group that resulted from uplift and the deep erosion, by at least , of the Vishnu Basement Rocks and any overlying strata. In the case of the unconformity between the Vishnu Basement Rocks and the Unkar Group, studies of the underlying Vishnu Basement Rocks indicate they were uplifted from a depth of about to a depth of about , between 1.75 and 1.66 billion years ago, and from a depth of about to the weathered surface on which the Bass Formation of the Unkar Group accumulated - between 1.66 and 1.25 billion years ago.Timmons, JM, KE Karlstrom, MT Heizler, SA Bowring, GE Gehrels, and LJ Crossey (2005) Tectonic inferences from the ca. 1254-1100 Ma Unkar Group and Nankoweap Formation, Grand Canyon: Intracratonic deformation and basin formation during protracted Grenville orogenesis.
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Many different types of uranium deposits have been discovered and mined. There are mainly three types of uranium deposits including unconformity-type deposits, namely paleoplacer deposits and sandstone-type also known as roll front type deposits. Uranium deposits are classified into 15 categories according to their geological setting and the type of rock in which they are found. This geological classification system is determined by the International Atomic Energy Agency (IAEA).
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87(8): 1299–1321. Close-up Major unconformities separate the Unkar Group from the strata overlying and underlying it. First, the Unkar Group, as the bottom unit of the Grand Canyon Supergroup, lies directly upon deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks. Second, an angular unconformity, with a dip of less than 10°, separates the base of the Nankoweap Formation from the underlying Unkar Group.
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The Hoppin Formation contains fossil trilobites, hyolithids and volborthellids. It is capped off by non-fossiliferous red and green slate, 186 meters thick, followed by an angular unconformity with the younger Early Pennsylvanian Pondville Conglomerate. In total, a 244-meter thickness of the formation is exposed. In 1969, Boston College geologist, James Skehan, proposed that the unit might be related to the Manuels Brook section in southeastern Newfoundland.
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It is often studied by geologists due to the extreme old age of the Precambrian rocks exposed by the creek bed. The canyon's high walls are of three dominant rock types. The Cambrian to Ordovician Deadwood Shale at the bottom lies on an unconformity above Precambrian rock and can be identified by its brown color. It is multi-layered in appearance and ranges from 10 to 400 feet thick.
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14 The third member is a muscovite-rich phyllite with a pearly to greenish gray sheen containing small staurolite and garnet crystals.Montgomery 1953, p.15 The Rinconada Formation is separated from the overlying Pilar Formation by an unconformity representing a gap in geologic time of 200 million years. The Rinconada Formation is interpreted as deltaic, fluvial, and shallow marine deposition of the regressive sequence of a marine transgression.
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The property is owned by the monarch as part of the Duchy of Lancaster holdings, but is administered by Harrogate Borough Council. Crags below Knaresborough Castle. There is an unconformity between mid- Carboniferous sandstones at the road level and late Permian grits and limestones above. Knaresborough castle has had ravens since 2000, one of which was donated by the Tower of London, and another an African pied crow named Mourdour.
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Clastic sequences continued to form in the Paleogene, the first 43 million years of the Cenozoic. Within that time frame, an unconformity emerged, in which Paleocene and Eocene sediments sit directly atop units from the Cretaceous. Sediments from the Pleistocene and Holocene, in the last 2.5 million years of the Quaternary are found in large sand dunes in southeastern Western Sahara as well as large lake beds throughout the country.
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Mayuga, M.N., pp. 167-169. Basement consists of the Catalina Schist and is overlain with up to 8,000 feet of Miocene and Pliocene sediments, the main oil producing zones being the Puente and Repetto sandstones.Mayuga, M.N., pp. 163-164. An unconformity in the Pliocene between the Repetto and the Pico indicates the top of the structure was eroded to a flat surface and later Pliocene and Holocene sediments were deposited horizontally.
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The Seaspray Group lies unconformably above the Latrobe Group, and was deposited in the Oligocene to the Miocene. This group makes up the majority of the seals in the region due to the unconformity with the Latrobe Group, as well as the low permeability of the rock types, which include shales, marls, limestones, calcareous claystones, siltstones, and sandstones. The typical depositional environments of these rock types, are low energy marine environments.
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Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation. The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together.
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The geology of Brunei is primarily made up of Cenozoic rocks overlying deeper rock units on the island of Borneo. Rocks from the Oligocene through the Holocene are up to 15 kilometers thick. The oldest rocks are part of the Meligan Formation and Temburong Formation in the east and are the deformed remnants of floodplain sediments. An unconformity separates the older rocks from younger Middle Miocene and Pliocene rocks.
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The Latrobe Group found in the Otway Basin, closer to Victoria, is from the same time and produces the oil found in the area. From Late Paleocene to early Eocene there was an unconformity. A shale from Demons Bluff Formation follows in the Eocene, deposited in calm sea water. The Torquay Group reaches from Oligocene to the current day, with marl and limestone formed in open sea water.
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A long period of uplift and erosion was concurrent with and followed the above events, creating a major unconformity, which is a large gap in the geologic record. Sediments worn off the Death Valley region were carried both east and west by wind and water. No Jurassic- to Eocene-aged sedimentary formations exist in the area, except for some possibly Jurassic-age volcanic rocks (see the top of the timescale image).
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Located less than one mile northwest of the Great Unconformity on Southington Mountain is Hushak Rock, known informally for decades as White Rock. The overlook has expansive views of the region and can be seen from much of Route 229 and area neighborhoods. The state of Connecticut officially named Hushak Rock in 2017 for longtime Southington civic leader and World War II pilot Walter J. Hushak (b. 1923).
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The Nankoweap is only exposed in the eastern part of the canyon. A gap in the geologic record, an unconformity, follows the Nankoweap. Sixtymile Formation is the last rock unit in the Chuar Group All formations in the Chuar Group were deposited in coastal and shallow sea environments about 1000 to 700 million years ago. The Galeros Formation is a mainly greenish formation composed of interbedded sandstone, limestone, and shale.
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The next two periods of geologic history, the Ordovician and the Silurian, are missing from the Grand Canyon sequence. Geologists do not know if sediments were deposited in these periods and were later removed by erosion or if they were never deposited in the first place. Either way, this break in the geologic history of the area spans about 65 million years. A type of unconformity called a disconformity was formed.
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Today, the Coconino is a thick golden white to cream- colored cliff-former near the canyon's rim. Cross bedding patterns of the frosted, fine-grained, well-sorted and rounded quartz grains seen in its cliffs is compatible with but does not substantiate conclusively an eolian environment. Also fossilized are tracks from lizard-like creatures and what look like tracks from millipedes and scorpions. An unconformity marks the top of this formation.
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Contact with Tonoloway Formation is probably conformable, but sharp enough to suggest an unconformity. Upper contact with the Old Port Formation is conformable. The Keyser was divided into three members by J. W. Head in 1972.Head, J.W., III, 1972, Upper Silurian-Lower Devonian stratigraphy and nomenclature in the central Appalachians, IN Guidebook for the 37th annual field conference of Pennsylvania geologists: Field Conference of Pennsylvania Geologists, no.
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Neumann et al., 2003, p.91 Data collected from outcrops and boreholes indicate that the Ipubi Formation is separated from the underlying Crato Formation and the overlying Romualdo Formation by regional unconformities in proximal domains. The lower unconformity separates the top of the Crato Formation, which is mainly represented by its uppermost interval of laminated limestones (C6), from the basal black shales and claystone deposits of the Ipubi Formation.
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The transition from the top of the Borrowdale Volcanics into the overlying Dent Group is marked by an unconformity. The Dent Group is of latest Ordovician age and forms the lowermost part of the Windermere Supergroup. It was deposited in shallow marine conditions, consisting mainly of calcareous mudstones, siltstones, limestones and shales. There is evidence of continued volcanism, with tuffs locally developed at various levels within the group.
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This erosional event removed any Silurian and Devonian rocks that may have been present.Henry, 1982 The Barnett Shale was deposited over the resulting unconformity. Provenance of the terrigenous material that constitutes the Barnett Shale was from Ouachita thrust sheets and the reactivation of older structures such as the Muenster Arch. Post-Barnett deposition continued without interruption as a sequence of extremely hard and dense limestones were laid down.
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According to Steno's principle of original horizontality, sedimentary rocks are normally deposited as horizontal layers. When tectonic movement occurs sedimentary layers can be tilted. under such circumstances, the sedimentary planes will have a dip (an angle with a horizontal reference plane). When new sedimentary layers are deposited on top of tilted ones, they will have an angle with the older ones, a structure which is called an angular unconformity.
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For a time climatic conditions became wetter and streams cut channels through the sand dunes, forming the Kayenta Formation. Arid conditions returned to the region with a vengeance; a large desert spread over much of western North America and later became the Navajo Sandstone. A fourth unconformity was created by a period of erosion. Mud flats returned, forming the Carmel Formation, and the Entrada Sandstone was laid down next.
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It contains very little organic matter, and abundant sea urchin fossils. The Kamp Ranch Limestone is found above the unconformity in the Dallas area. It is similar to the older Six Flags and Bluebonnet Limestones, as it is predominantly composed of disaggregated prisms of Inoceramus clamsReid, W. T. (1952) Clastic limestone in the Upper Eagle Ford Shale, Dallas County, Texas: Field and Laboratory, v. 20, p. 111–122.
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Eubrontes, a dinosaur footprint in the Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah. The Moenave Formation is a Mesozoic geologic formation, in the Glen Canyon Group. It is found in Utah and Arizona. The Moenave was deposited on an erosion surface on the Chinle Formation following an early Jurassic uplift and unconformity that represents about ten million years of missing sedimentation.
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The depositional environment of the Cuche Formation has been analysed to be a low-energy tidal-dominated deltaic setting, with frequent marine incursions into continental and lagoonal areas marked by the presence of both the flora and the many fish species found in the formation The Cuche Formation in some places discordantly and in other areas transitionally defined by colour changes,Rodríguez & Solano, 2000, p.58Mojica & Villarroel, 1984, p.67 overlies the Floresta Formation in Boyacá and the Mogotes Formation in Santander,Rodríguez Gutiérrez, 2017, p.75 and is, by an angular unconformity up to 60 degrees,Mojica & Villarroel, 1984, p.68 overlain by the Upper Jurassic Girón,Rodríguez & Solano, 2000, p.41 and Early Cretaceous Tibasosa Formations.Mojica & Villarroel, 1984, p.65 The angular unconformity between the Paleozoic and Mesozoic is exposed along the road between Duitama and Sogamoso, and is the location where the first flora fossils were found in 1978.
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Hutton then sought evidence to support his idea that there must have been repeated cycles, each involving deposition on the seabed, uplift with tilting and erosion, and then moving undersea again for further layers to be deposited. At Glen Tilt in the Cairngorm mountains he found granite penetrating metamorphic schists, in a way which indicated to him that the presumed primordial rock had been molten after the strata had formed. He had read about angular unconformities as interpreted by Neptunists, and found an unconformity at Jedburgh where layers of greywacke in the lower layers of the cliff face have been tilted almost vertically before being eroded to form a level plane, under horizontal layers of Old Red Sandstone. In the spring of 1788 he took a boat trip along the Berwickshire coast with John Playfair and the geologist Sir James Hall, and found a dramatic unconformity showing the same sequence at Siccar Point.
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The center of the basin was uplifted by the Hercynian orogeny to form the Hoggar Mountains. Sedimentary rocks from the Paleozoic, thicken toward the mountains and to the south. East of Tamesna, Cambrian and Ordovician sedimentary rocks are up to 500 meters thick and include conglomerates and sandstones. There is an unconformity between these deposits and glacial sediments, associated with the widespread glaciation and global cooling of the Ordovician-Silurian extinction event.
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2011 The formation is thought to be separated from the underlying lower Vadito Group by a significant unconformity. It is overlain by the Ortega Formation. Based on uranium-lead dating of zircons, the age of the formation is 1.693 Mya, and it is interpreted as metamorphosed rhyolites from the waning stage of back arc rifting associated with the Yavapai orogeny. It likely correlates with the Burned Mountain Formation in the Tusas Mountains.
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The top of the structural trap is marked by a pre-Pennsylvanian unconformity with sediments subcropping against the Oswego Lime.Gatewood L.E., 1970, Oklahoma City Field - Anatomy of a Giant, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, p. 227. The sedimentary section starts with the Arbuckle Dolomite overlain by Simpson strata, which includes the Oil Creek, McLish, Tulip Creek, and Wilcox sandstones, of Ordovician age, with the Wilcox being the most productive zone.
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After the deposition of the pre-Turonian units, there was a large emergence and erosion that can be observed as a major unconformity at the base of the middle Miocene units. Emergence did not occur at the same rate or in all sections of the basin. During this time, the basin was covered by a marine embayment. Rivers sourced in the highlands brought large amounts of detritus to the northeastern edge of the basin.
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The Sespe Formation is the first to appear above the "Great Unconformity" and is marked by interbedded mudstones, sandstones and pebbly sandstones. This bed sequence indicates an alluvial fan, meandering stream or braided stream origin. Upward from the Sespe Formation toward the Vaqueros, the grains become finer and the beds become thinner; indicating a transition to a shallow marine environment. The Vaqueros Formation is marked by two sandstone, siltstone and shale units.
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There are also characteristic mollusk fossils that indicate the area was dominately shallow marine. The Topanga Group is the next major formation in the stratigraphic sequence and infills the topography on older rocks. It is a mixed sedimentary and volcanic unit whose base is an erosional unconformity. The unit consists of 3 parts: First is a basal marine conglomeratic sandstone, followed by a dominantly basaltic middle layer of multiple submarine lava flows and tuffs.
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15 In this part, the formation is overlain by the Río Negro and Tibú-Mercedes Formations. In the central area at the type locality in the Lebrija River valley, the formation unconformably overlies the Bocas Formation and is overlain by the Tambor Formation. On the Mesa de Los Santos and the Bucaramanga Massif, the formation overlies the Jordán Formation with an angular unconformity dipping 10 to 15°.Ayala et al., 2005, p.
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The upper and lower contacts of the Redwall Limestone are both unconformities. Locally, the Redwall Limestone directly overlies the unconformity that forms its lower contact consisting of a basal conglomerate. This basal conglomerate is typically composed of gravel that is locally derived from either the underlying Temple Butte Formation or Muav Limestone. The Temple Butte Formation consists of a thin layer of Devonian strata that fills paleovalleys cut into the underlying Cambrian Muav Limestone.
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Land reclamation off the coast has added 400 hectares of land and 30 km of coastline. Half of the 22 km² of surface area which Hamad International Airport was constructed on was reclaimed land. The geology of Doha is primarily composed of weathered unconformity on the top of the Eocene period Dammam Formation, forming dolomitic limestone. Pearl is a purpose-built artificial island off the coast of Doha, connected to the mainland by a bridge.
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Subduction in Late Paleozoic Above the angular unconformity, the Carboniferous and Permian units lied conformably with each other, both having similar characteristics in the rock layers. They showed low-grade metamorphism in siliciclastic and carbonate sedimentary rocks deposited in shallow to deep marine environment with fine-to-medium grain size. Also, there were granites (syenogranites and monzogranites) intruded at the age of ca. 300–250 Ma. They were generally seen with foliations as well.
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Rifle Butts Quarry is a Site of Special Scientific Interest (SSSI) in the East Riding of Yorkshire, England. The particular interest of this reserve is the geological feature exposed on the quarry face. The site is owned by the Yorkshire Wildlife Trust. The exposure which is identified as being of national importance in the Geological Conservation Review shows a Cretaceous unconformity, where sediments from the Jurassic and Lower Cretaceous periods were eroded away.
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Belmont: West Publishing Company, 1997, pp. 112 - 113 Thus, a transgression reveals itself in the sedimentary column when there is a change from nearshore facies (such as sandstone) to offshore ones (such as marl), from the oldest to the youngest rocks. A regression will feature the opposite pattern, with offshore facies changing to nearshore ones. The strata represent regressions less clearly, as their upper layers are often marked by an erosional unconformity.
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Subsidence of the region occurred as the continental crust thinned and the newly formed Pacific widened, forming the Ibex Formation. An angular unconformity (an uneven gap in the geologic record) followed. A true ocean basin developed to the west, breaking all the earlier formations along a steep front. A wedge of clastic sediment then began to accumulate at the base of the two underwater precipices, starting the formation of opposing continental shelves.
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These sediments were deposited on flood plains by streams on an expansive lowland that was slightly sloped in the direction of an ocean to the west. Mud built up in tidal flats to become the mudstone of Moenkopi Formation. Examples of this formation, some that still show fossilized ripple marks and mudcracks, can be seen in the northern and western parts of the park. Another period of erosion returned, creating a third unconformity.
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The Salle de la Verna has formed where the river flows off the schist onto Devonian limestone. Over time, the river found a route through the soluble limestones, leaving the original downstream river passage (the Gallerie Aranzadi) high and dry. The chamber was formed by a process of solution and collapse, beginning about 200,000 years ago. The unconformity between the Paleozoic and Mesozoic rocks is clearly exposed in the walls of the chamber.
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Geological Society of America Bulletin, 96(12), pp.1572-1579. The Proterozoic rocks that underlie the Lake Nipigon region contain a variety of mineral resources. Although economic deposits have yet to be found, 1.53 billion-year- old anorogenic granites within the Lake Nipigon area potentially contain yttrium, zirconium, rare earth elements and tin mineralization. The clastic sedimentary rocks of the Sibley Group, are host to unconformity-related uranium and redbed-type copper ore deposits.
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An unconformity marks the top of this formation. One of the highest, and therefore youngest, formations seen in the Grand Canyon area is the Kaibab Limestone (see 6d in figure 1). It erodes into ledgy cliffs that are thick and was laid down in latest early Permian time, about 270 million years ago, by an advancing warm, shallow sea. The formation is typically made of sandy limestone sitting on top of a layer of sandstone.
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At the end of the Taconic orogeny, an unconformity appears with the uplift and erosion of the massive delta. In the Silurian and Devonian, new sediments covered the erosional surface, beginning with the white quartz pebbles of the Shawangunk conglomerate. Crustal stretching created a series horst and graben features, which remain in the Adirondacks as well as in the Mohawk, Hudson and Champlain areas. Down-dropped grabens preserved Ordovician rock from erosion.
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Up to 13,000 feet of sedimentary rocks accumulated in the Oquirrh Basin. A small unconformity separates these rocks from those formed in the Permian. These rocks tend to be difficult to correlate, with significant lateral variation, cross-bedded sandstones indicating wing transportation and a lack of late Permian rocks. A major marine transgression generated the Kaibab Limestone (the rimrock of the Grand Canyon), represented by the Park City and Phosphoria groups in Utah.
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The top of the coal measures may be marked by an unconformity, the overlying rocks being Permian or later in age. In some parts of Britain, however, the Coal Measures grade up into mainly coal-barren red beds of late Westphalian and possibly Stephanian age. Within the Pennine Basin these barren measures are now referred to as the Warwickshire Group, from the district where they achieve their thickest development.Powell, J.H. et al. 2000.
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In the Paleozoic, the supercontinents Gondwana and Laurussia were separated by the Rheic Ocean. These supercontinents converged, closing the Rheic Ocean and resulting in the mountain uplift of the Hercynian orogeny. Geologists have recognized rock deformation and a stratigraphic unconformity dating to the Hercynian orogeny and spanning the margins of the African and Arabian plates, including Lebanon. The region was situated on the northern shore of Gondwana, adjacent to the Paleo-Tethys Ocean.
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The Absaroka sequence was a cratonic sequence that extended from the end of the Mississippian through the Permian periods. It is the unconformity between this sequence and the preceding Kaskaskia that divides the Carboniferous into the Mississippian and Pennsylvanian periods in North America. Like the Kaskaskia sequence, Absaroka sedimentary deposits were dominated by detrital or siliclastic rocks. The first sediments were deposited near the continental margins, particularly near the Ouachita and Appalachian highlands.
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The Río Colorado Subgroup, formerly named as Río Colorado Formation, is a Late Cretaceous (Santonian to Early Campanian) geologic subgroup of the Neuquén Basin in northern Patagonia, Argentina. It belongs to the Neuquén Group and contains the Anacleto and Bajo de la Carpa Formations. The subgroup overlies the Río Neuquén Subgroup and is overlain by the Allen Formation of the Malargüe Group, separated by an unconformity dated to 79 Ma.Leanza et al., 2004, p.
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It contains volcanic tephra with an age of 6.8 to 7.1 Ma, identical to the Peralta Tuff Member of the Bearhead Rhyolite. The similarity in age with the Navajo Draw Member suggests the two members interfinger. The Picuda Peak Member is mostly reddish sandy conglomerate and arkosic sandstone. It contains beds formerly assigned to the Ceja Formation but which are now known to lie below the Rincones paleosurface, a major regional unconformity.
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Above the Dagorda formation is the post-rift carbonate shelf environment—the Coimbra dolomite, Brenha limestone, and Cardieros carbonate grainstone. A substantial unconformity, associated with significant tectonic activity, characterizes the top of the sequence. The carbonate shelf environment is still present in the Upper Jurassic—characterized by the Montejunto grainstone and reef facies, Cabacos organic-rich limestone (capped by anhydrite). Above this sequence, deposition is dominated by the siliciclastics from the Meseta highlands.
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The Quebrada del Barro Formation is a geological formation of the Marayes-El Carrizal Basin in San Juan Province, Argentina. This formation is the most fossiliferous portion of the Triassic Marayes Group, and is also the youngest unit of the group, overlying the El Carrizal Formation. An unconformity at the top of the Quebrada del Barro Formation separates it from the Cretaceous-age Los Riscos Formation of the El Gigante Group.Gardini et al.
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Topography of Libya The Sarir stratigraphic column generally resembles succession patterns throughout the Sirte Basin, with some variations. In the early regressive phase, basal sandstones were deposited on a Precambrian basement of igneous and metamorphic rocks. Sandstones are dated on angiosperm pollen as younger than Albian, probably from the Late Cretaceous. After a lengthy hiatus, represented by unconformity and sandstone erosion, a transgressive sequence of red, green, and purple Anhydrite shales was laid.
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An angular unconformity separates the Eocene from the top section of the La Jolla Group. The Pliocene Aged San Diego Formation is composed of interbedded silt and sand. Some fossil bivalve shell layers can be found in the San Diego Formation which were deposited from a transport. The upper section of the La Jolla Group consists of Pleistocene aged marine terraces deposited during times of high sea level in between ice ages.
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Parotosuchus, an index fossil of the Yarenskian. The Yarenskian Gorizont ("Yarenskian Horizon") is a major biostratigraphic unit in Russia corresponding to Upper Olenekian-age terrestrial sediments. It lies above the Ustmylian Gorizont of the Vetlugian Supergorizont, and is located below a short unconformity overlain by the Donguz Gorizont. Some paleontologists elevate the Yarenskian to a supergorizont and subdivide it into two smaller units: the older Fedorovskian Gorizont and the younger Gamskian Gorizont.
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Some scientists believe Upheaval Dome was created from Paradox salt bed movement, creating a salt dome, but more modern studies show that the meteorite theory is more likely to be correct. A warm shallow sea again flooded the region near the end of the Pennsylvanian. Fossil-rich limestones, sandstones, and shales of the gray-colored Honaker Trail Formation resulted. A period of erosion then ensued, creating a break in the geologic record called an unconformity.
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In the type area there is an unconformity between the Arcadia Park and the underlying Britton Formation. The base of the Arcadia Park is a thin limestone termed the Kamp Ranch Limestone.Norton, G. H. (1965) Surface geology of Dallas County, in The geology of Dallas County: Dallas Geological Society, Dallas, Texas, p. 40–125. The Kamp Ranch Limestone is made up of broken pieces (prisms) of Inoceramus clams, and also contains shark's teeth.
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While the Hoko River formation overlies the Lyre Formation in many places, the two formations intertongue in others. The Makah and Hoko River formations are separated by a major unconformity. Calcareous clasts in the formation contain crab, gastropod, cephalopod, and wood fossils. Magnetostratigraphy performed in 2008 on samples taken from the type section of the Hoko River formation showed a correlation of age with either Chron C18r (40.0–41.2 Ma) or Chron C17r (38.0–38.2Ma).
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Eparchaean Unconformity of Detrital rocks of Tirumala Hills, Eastern Ghats India's geological features are classified based on their era of formation. The Precambrian formations of Cudappah and Vindhyan systems are spread out over the eastern and southern states. A small part of this period is spread over western and central India. The Paleozoic formations from the Cambrian, Ordovician, Silurian and Devonian system are found in the Western Himalaya region in Kashmir and Himachal Pradesh.
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These monadnocks served locally as sources of coarse-grained sediments during the marine transgression that deposited the Tapeats Sandstone (Tapeats Sea), and other members of the Tonto Group. Within the Unkar Group, the contact between the Hakatai Shale and overlying Shinumo Sandstone is a distinct disconformity. This contact is the only significant unconformity that occurs within the Unkar Group. This disconformity is sharp and locally truncates cross-bedding and channels exhibited by sandstones in the underlying Hakatai Shale.
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By comparison with neighbouring basins both Paleozoic and Mesozoic sequences are expected to be present in the Hatton Basin. The proven Cenozoic sequence starts with Paleocene lavas, part of the North Atlantic Igneous Province, overlain by Eocene claystones. There is then a major hiatus, with the next youngest preserved strata above the unconformity (known regionally as C30) being of Upper Eocene to Lower Oligocene age. The remainder of the sequence consists of Miocene to Pleistocene calcareous oozes.
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The Nyanzian Belt, by contrast, is mainly acid and basic basalt, dolerite, trachyte, rhyolite and tuff in separated zones south and east of Lake Victoria. The Kavirondian System is closely related to the Nyanzian, but separated by an unconformity and a zone of intense deformation. The Kavirondian is believed to be the remains of a molasse that formed by the Nyanzian as evidenced by sedimentary rocks such as mudstone, conglomerate as well as volcanics and grit.
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The hill ranges of the Tirumala rise to a height of (at Tirumala) from the average height of in the plains at Tirupati. The steep scarp of the ranges shows the Eparchian Unconformity's topographic, structural and denudational features. The sedimentary thickness of the Cudappah basin is of the order of , and includes volcanic sequences in the form of sills and dykes. A prominent Eparchaean Unconformity of the formation resting on the archaean peninsular gneissic complex is noted.
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Coquihalla Mountain, a volcanic peak in the Pemberton Volcanic Belt that was active during the early Miocene epoch. The Coquihalla Volcanic Complex began its formation when large pyroclastic flows were erupted on an erosional surface. Emptying of the shallow magma chamber caused tilting of the unconformity on the Eagle pluton, which is situated to the southeast. Concomitant with faulting, tilting and subsidence, avalanche breccias repeatedly slid off oversteepened exposures of the Pasayten Group and Eagle pluton.
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The sequence is broken down into two tectonostratigraphic intervals, thought to reflect two distinct rift phases. The lower unit is the Doswell Group, which has a more restricted extent, and comprises two formations, the South Anna Formation and the Falling Creek Formation. The upper unit, which is separated from the underlying Doswell Group by an unconformity, is the King George Group, which comprises three formations, the Newfound Formation, the Port Royal Formation and the Leedstown Formation.
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The foreland basin was characterized by an approximately 5-km (3.1-mi)-thick Eocene wedge of fluvial-deltaic sedimentation (Misoa Formation), where the most prolific hydrocarbon reservoirs of the Maracaibo Basin are concentrated. Fluvial and shallow-marine sedimentation continued in the south and southwest areas of the Maracaibo Basin. The Eocene unconformity represents the main seal above Eocene reservoirs, but it is locally breached by faulting, allowing the upward ascent of hydrocarbons into Miocene reservoirs at the basin edges.
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Sandstones are dated on angiosperm pollen as younger than Albian, probably from the Late Cretaceous. After a lengthy hiatus, represented by unconformity and sandstone erosion, a transgressive sequence of red, green, and purple Anhydrite shales was laid. Variegated bed remnants occur in crestal sections of many northern structures, such as in wells B-1-65 and C-1-80. Above the transgressive sequence are Late Cretaceous shales with tight, micritic carbonate, marking the top of the Mesozoic.
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Carlin Trend, shown with other alignments of sediment-hosted gold deposits in Nevada. Source: USGS. Newmont's Gold Quarry mine in 2009, on the Carlin Trend The Carlin Unconformity or Carlin Trend is a geologic feature in northeastern Nevada which represents a period of erosion or non-deposition likely associated with a collision between a tectonic crustal block called a terrane and the North American Plate. The collision occurred during the Mississippian Period, about 350 million years before present.
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Early Mississippian tuff, breccia, volcaniclastic sandstone and mafic volcanic rocks in the Skolai Group are the oldest rocks. The Skolai Group is separated from overlying Middle Triassic siltstone by a regional unconformity. Above the siltstone is the vast Nikolai Formation—basal conglomerate and basalt three kilometers thick, which extends far to the west into Alaska and as far south as Vancouver Island. It is interlayered with the Chitistone reef limestone and the deep marine McCarthy Formation.
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Temple Butte Formation is thick; thinner near Grand Canyon Village and thicker in western Grand Canyon. An unconformity representing 40 to 50 million years of lost geologic history marks the top of this formation. The next formation in the Grand Canyon geologic column is the cliff-forming Redwall Limestone, which is thick (see 4b in figure 1). Redwall is composed of thick-bedded, dark brown to bluish gray limestone and dolomite with white chert nodules mixed in.
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This is the cream to grayish-white rock that park visitors stand on while viewing the canyon from both rims. It is also the surface rock covering much of the Kaibab Plateau just north of the canyon and the Coconino Plateau immediately south. Shark teeth have been found in this formation as well as abundant fossils of marine invertebrates such as brachiopods, corals, mollusks, sea lilies, and worms. An unconformity marks the top of this formation.
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Carboniferous Limestone exposed near Ogmore-by-Sea showing the Carboniferous/Jurassic unconformity. The rocks exposed along the stretch of coast near Ogmore-by-Sea were laid down between 340 and 195 million years ago. They are all sedimentary rocks, originally deposited as lime, mud, sand and coarse pebbles, and over long periods of time these were compacted and solidified into limestone, shale and conglomerate. The oldest rocks are hard, grey limestones that make up the Carboniferous Limestone.
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In the type location there is about 60 metres of non-calcareous sandy shale and dark grey shale with beds of fine- grained sandstone. Between Kings Avenue and Commonwealth Avenue, there is a good outcrop on State Circle, consisting of buff-coloured laminated siltstone and shale with fine sandstone beds contorted by slumping. Its top is an unconformity, with Camp Hill Sandstone lying on top. There is probably up to 200 metres thickness of this shale.
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Typically the Onate Formation consists of about of orange yellow-weathering dolomitic siltstone with shales and sandstone. The base of the formation is a profound regional unconformity, so that the formation rest on either the Fusselman Formation or the Montoya Group. It is overlain by the Sly Gap Formation and thins to the north and south. The formation is interpreted as having been deposited on a shallow shelf environment deepening to a euxenic basin to the south.
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Muhos in the northeastern Gulf of Bothnia is a site of Jotnian sediment occurrence. At this location Jotnian sediments can be found within the Muhos Graben that has had a downward displacement of about one kilometre. The sediments in the Muhos Graben at the bottom are conglomerates and arkoses whose contact with the underlying metamorphic rocks constitute an unconformity. The pebbles of the conglomerate are made of schist and granite while the matrix is made of arkose.
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These ancient hills, which are ridges formed by block faulting, are up to tall. Thin drapes of Tapeats Sandstone of the Tonto Group either cover or drape onto most of these ancient monadnocks. However, the summits of the highest monadnocks protrude up through the base layer Tapeats Sandstone and are blanketed by overlying Bright Angel Shale as can be seen at Isis Temple. Lava Butte is a partially exhumed prehistoric monadnock associated with this unconformity that consists of Cardenas Basalt.
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Rocks of probable lower Devonian age are exposed near Yesnaby, on western Mainland. A ridge of granitic basement divides the Hara Ebb Formation, a sequence of breccias, conglomerates and sandstones deposited in an alluvial fan setting, from the Yesnaby Sandstone which was deposited in an aeolian setting.Lower Devonian of Orkney, Hall, Adrian and Brown, John, "Orkney Landscapes" (online) (Edinburgh, Scotland) September 2005, Last update 10-Nov-2008 The contact with the overlying Middle Devonian lacustrine Lower Stromness Flagstones is an angular unconformity.
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The Mangbei Basin, Douala Basin and Rio-del-Rey Basin formed in CAMZ and filled with Early Paleozoic volcanic and sedimentary rocks. The Douala and Rio-del-Rey basins both formed as a result of the breakup of the supercontinent Pangaea and the opening of the Atlantic Ocean. The conglomerate and sandstone of Mudeck Formation probably formed in the Early Cretaceous and is overlain by fossil-bearing shale. There is an unconformity between the crystalline basement rock and the Mudeck Formation.
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The Trujillo Sandstone, channel-deposits, and Cooper Canyon Formation, overbank deposits with minor channel and lacustrine deposits, are separated from the Santa Rosa-Tecovas by an unconformity. In eastern New Mexico, the Redonda Formation overlies the Cooper Canyon Formation. The Redonda has gradational eastward transition into the upper Cooper Canyon Formation. The Santa Rosa-Tecovas sequence has sediments made up of clasts derived from the north, northeast, and east of the Dockum, very similar to clasts found in the lower Chinle.
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A thin layer of Pleistocene sediments known as the Santa Barbara Formation lies between the Monterey and ground surface. Underneath the Vaqueros formation and separated by an unconformity is the Oligocene-age Sespe Formation; no oil has been found in or beneath this unit, even though one well had been drilled into it to a total depth of over .DOGGR, 278-9 The Sespe and Vaqueros Formations together form the second-most-prolific oil-producing unit in Southern California.James M. Galloway.
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The Baie Verte Peninsula is a large peninsula on the north east coast of the island of Newfoundland in the Canadian province of Newfoundland and Labrador. The Baie Verte Peninsula is a geologically complex area on the northwest coast of Newfoundland. The region is composed of multiple geological domains and has undergone extensive tectonic activity, uplift, and deformation, producing multiple unconformity surfaces. In addition, multiple phases of intrusion, some with volcanic cover sequences, add to the complexity of the geological model.
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The Sugarloaf A second period of erosion began around 250Ma which removed most of the Permian sediments in the region with the exception of some that were protected by the Hallett cove basin. This forms the second unconformity that separates the Permian from the Pliocene deposits. By the Cenozoic, the Mt Lofty Ranges had worn down to sea level. A period of faulting commenced which uplifted the ranges and downthrust the plains which, beginning 50Ma was flooded by the sea.
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The Bighorns were uplifted during the Laramide orogeny beginning approximately 70 million years ago. They consist of over of sedimentary rock strata laid down before mountain-building began: the predominantly marine and near-shore sedimentary layers range from the Cambrian through the Lower Cretaceous, and are often rich in fossils. There is an unconformity where Silurian strata were exposed to erosion and are missing. The granite bedrock below these sedentary layers is now exposed along the crest of the Bighorns.
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The Nama Group is a megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two early basins, the Zaris and Witputs, to the north, while the South African Vanrhynsdorp Group was deposited in the southern third.Gresse, P. G., G. J. B. Germs. The Nama foreland basin: sedimentation, major unconformity bounded sequences and multisided active margin advance.
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Location of Tendaguru in Tanzania The Tendaguru Formation, or Tendaguru Beds are a highly fossiliferous formation and Lagerstätte in southeastern Tanzania. The formation represents the oldest sedimentary unit of the Mandawa Basin, overlying Neoproterozoic basement, separating by a long hiatus and unconformity. The formation reaches a total sedimentary thickness of more than . The formation ranges in age from the late Middle Jurassic to the early Early Cretaceous, Oxfordian to Hauterivian stages, with the base of the formation possibly extending into the Callovian.
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Those Famennian strata represent the top of the Paleozoic series pleated with north dipping. Above, the transgressive Upper Cretaceous overlies horizontally with unconformity. It includes from the bottom to the top a paleozoic boulder conglomerate mixed with a sandy and glauconitic marl matrix, coarse clayey and glauconitic sands, containing Chlamys asper, Ostrea diluviana, Praeactinocamax plenus and finally marl with Terebratulina gracilis. These strata belong to the Cenomanian- Turonian and were deposited between 90 and 100 million years ago, during a transgressive phase.
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Geology of the Florissant Fossil Beds National Monument. Field Guide, 9 pages The massive unconformity is due to erosion that occurred during the uplift of the modern Rocky Mountains, the Laramide Orogeny.Steven, T. A. (1997). Middle and Late Cenozoic Tectonic and Geomorphic Development of the Front Range of Colorado. Rocky Mountain Association of Geologists, 1997, Colorado Front Range Guide Book, p. 115-125 The Wall Mountain Tuff was deposited as a result of a large eruption from a distant caldera.
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In the root zone, mantle-derived magma underwent fractional crystallisation which was followed by mingling between the residual liquids and melts generated by anatexis of the surrounding gneissic basement. It is divided into eastern Dharwar Craton and western Dharwar Craton owing to their differences in lithologies and ages. The term Dharwar Supergroup is now used as synonymous with metamorphosed Precambrian sediments and including all the schistose series below the Eparchaean Unconformity. The Dharwarian rocks are mostly unfossiliferous except for the stromatolitic limestones.
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These features are only present proximal to subducted seamounts, and absent where there are no subducted seamounts. The accretionary wedge of the Manila Trench broadens going north; seeing as the southern section of the margin accumulates more trench-fill sediments than the north. The trench-fill sediments are thought to be sourced from the collisional zone of the Taiwan orogeny or by gravity controlled processes. The sequence boundary ‘t0’ represents the unconformity between the hemipelagic sediments and overlying trench-fill sediments.
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The Bajada Colorada Formation overlies the Quintuco and Picún Leufú Formations. At its top, it is separated by the overlying Agrio Formation by an unconformity (sedimentation hiatus) that has been dated at 134 mya. Bajadasaurus stems from the Bajada Colorada locality, the type locality of the formation. The locality yielded the remains of another sauropod, the diplodocid Leinkupal laticauda, as well as of several species of theropod that can be ascribed to basal tetanurans and possibly to abelisauroids and deinonychosaurians.
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During the Damian Stage, carbonate deposit stopped, bringing an erosional unconformity. As the Selandian transgressive phase got underway glauconite sand and older, reworked Cretaceous and Devonian sediments deposited, overlain by pelagic smectite clay. Erosion in the Neogene and Pleistocene has eroded most rock units that would likely have indicated open marine conditions. A break in sedimentation in the Oligocene was followed by a marine transgression and sediment accumulated in the Danish Basin, with significant coarse quartz sand compared to older Paleogene clays.
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Late Devonian rocks are not present and an unconformity and conglomerate deposits point to a break in sedimentation. Tournaisian and Westphalian calcareous rocks from Carboniferous are distributed across the west, ranging from 350 meters thick at Herat to 400 meters at Kotale Shutur Chun. These rocks grade to quartzite and shale to the east. In the upper Kabul valley and Dash-t-Nawar, early Carboniferous limestone is 100 to 420 meters thick, disconformably overlain by 1.5 kilometers of quartzite and shale.
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New Siberia Island consists of clastic sediments ranging from Late Cretaceous to Pleistocene in age. The Late Cretaceous sediments consist of extensively folded layers of gray and greenish gray tuffaceous sand, tuffaceous silt, pebbly sand, and layers of brown coal exposed in sea cliffs along it southwest coast. The sand and silt often contain either volcanic glass, fossil plants, rhyolite pebbles, or some combination of them. Eocene sand, silt, clay, and brown coal overlies an erosional unconformity cut into the Late Cretaceous sediments.
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They lie upon an angular unconformity which cuts across pre-basin strata. Lacustrine sediments of the Lower Tinajani Formation, which are exposed within the Tinajani Basin, demonstrate the presence of a pre-Quaternary, ancestral Lake Titicaca within it between 18 and 14 million years ago (Mya).Marocco, R., R. Baudino, and A. Lavenu, 1995, Intermontane Late Paleogene–Neogene Basins of the Andes of Ecuador and Peru: Sedimentologic and Tectonic Characteristics. in A.J. Tankard, R. Suárez Soruco, and H.J. Welsink, eds.
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Geology of National Parks, page 52 Compression from the Laramide event deformed the land in the area to form the up to 5° dipping Bryce Canyon Anticline. All of the Canaan Peak, Pine Hollow, Kaiparowits, and Waheap formations, along with part of the underlying Straight Cliffs, were removed from the anticline's crest by erosion before the Claron Formation was deposited.Davis and Pollock (2003). Geology of Bryce Canyon National Park, page 53 An angular unconformity therefore exists along the anticline's crest.
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This led to the formation of a back arc basin, the Black Sea. The start of this subduction is responsible for the unconformity between the Kilimi and Cemaller formations and marks the beginning of the Alpide orogeny in the region. The andesitic volcaniclastic sediments of the Yemislicay support the subduction of oceanic crust in the region during this time. The Zonguldak basin was able to sustain deposition after the start of the Alpide orogeny due to rifting in the Black Sea basin.
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South and east of the Grand Canyon, the evaporites and contorted sandstones (sabkha deposits) of Toroweap Formation interfinger with and are replaced by cross- bedded sandstones of the Coconino Sandstone. As a result, the Kaibab Limestone directly overlies the Coconino Sandstone in the Mogollon Rim region. The Kaibab Limestone directly overlies the White Rim Sandstone in northeastern Arizona and southeastern Utah. The upper contact of the Kaibab Limestone (Harrisburg Member) with the overlying Moenkopi Formation is an erosional unconformity and disconformity.
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Western extension of Whatley Quarry. Whatley Quarry, is a limestone quarry owned by Hanson plc, near the village of Whatley on the Mendip Hills, Somerset, England. The quarry exhibits pale to dark grey Carboniferous Limestone with small area of overlying horizontally bedded buff-coloured Jurassic oolitic limestone forming an angular unconformity, with extensive dolomitisation of top of the Black Rock Limestone. There are abundant near- vertical fissures and joints near top of limestone with karst weathering and minor pinnacle formation.
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At the terminus advance of former glaciers marine terraces can be correlated by their size, as their width decreases with age due to the slowly thawing glaciers along the coast line. The lithostratigraphic approach uses typical sequences of sediment and rock strata to prove sea level fluctuations on the basis of an alternation of terrestrial and marine sediments or littoral and shallow marine sediments. Those strata show typical layers of transgressive and regressive patterns. However, an unconformity in the sediment sequence might make this analysis difficult.
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The Midden Curaçao Formation probably formed in the Paleocene based on poorly preserved foraminifera fossils. There is an unconformity between Cretaceous rocks and this formation, which includes remnants of submarine fan deposits along with andesite metamorphosed to greenschist grade. Parts of the formation date to the Eocene, while the upper units formed in the Oligocene. Together with the Knip Group, the Midden Curaçao Formation is intruded by intermediate igneous rocks, which caused contact metamorphism up to zeolite grade on the sequence of metamorphic facies.
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Kimberley Brewery was taken over by Greene King in 2006, another major brewer in a multimillion-pound deal which marked the end of the traditional Kimberley Ales as ale brewing ceased shortly afterwards and only a distribution centre remained there. The former Kimberley Brewery site has within its boundaries a geological Site of Special Scientific Interest (SSSI). It is listed under the title of "Kimberley Railway Cutting" as an important location for Permian Gymnosperm fossils. The Permian - Carboniferous unconformity can be found in the Kimberley Railway Cutting.
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The collisions, which welded the plates to the continent, folded the Cleopatra tuff in such a way that the two ore bodies ended up on opposite sides of a fold called the Jerome anticline. No record exists for the next 1.2billion years of Jerome's geologic history. Evidence from the Grand Canyon, further north in Arizona, suggests that thick layers of sediment may have been laid down atop the ore bodies and later eroded away. The gap in the rock record has been called the Great Unconformity.
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It is exposed as a topographic bench 1200 feet (365 m) below the top of Island in the Sky (thus earning its name) and along the White Rim Road. A fossilized offshore sand bar made of the White Cliff Sandstone is also exposed in the Elaterite Basin. A tarry dark-brown oil called elaterite seeps out of the structure, giving the basin its name. The Permian sea retreated, which exposed the land to a long period of erosion and thus created a second unconformity.
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The collision of the terrane spurred the Romanzof orogeny, uplifting the rocks and driving erosion, leading to a Mississippian unconformity. The thickening of the crust during the orogeny caused melting and granite intrusions visible at Hoidahl Mountain, Old Crow Range and Mount Sedgwick. Around the same time in the mid-Paleozoic, the "Intermontane terranes" that underlie the Yukon Plateau in the central part of the territory were added to the Laurentian margin. Most of the terranes originated as part of the Panthalassa Ocean, the proto-Pacific Ocean.
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A significant unconformity separates the Blairmore Group from overlying rocks. During the Cenomanian and Albian, the connection with the Arctic Ocean was nearly severed, creating the Mowry sea, which developed its own endemic group of ammonites. Fossils across western Canada with both exotic and endemic fish scales and ammonites indicates that the Gulf of Mexico flooded the area from the south. The sea filled with fine sediments of the Colorado Group concurrent with the deposition of clastic and volcanic sediments in the Mill Creek Formation.
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The Stillwater Complex, by contrast, is made up of ultrabasic igneous rocks exposed at the surface in Park, Stillwater, and Sweet Grass Counties. Together, these three rock formations formed between 2.54 and 1.69 billion years ago. The Pony Group and Cherry Creek Group are overlain by the Belt Series sedimentary rocks, which deposited after a period of erosion that left a large unconformity. These shallow water rocks from the Neoproterozoic range between 35,000 and 50,000 feet thick, overlain by additional Middle Cambrian sedimentary rocks.
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The Sub-Paleogene surface is an ancient erosion surface that exist in southern England. In parts the Sub-Paleogene surface appear as tilted plain and parts as an unconformity beneath sediments of Paleogene age. The surface was formed by the erosion of chalklands in England following a regression in the Maastrichtian age. The time during which the surface formed has been estimated by comparing the age of the last Maastrichtian chalk to deposit and the age of the earliest Paleogene sediment to cover the surface.
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These monadnocks served locally as sources of coarse-grained sediments that accumulated during the marine transgression to form the Tonto Group.Sharp, RP (1940) Ep-Archean and Ep-Algonkian erosion surfaces, Grand Canyon, Arizona. Geological Society of America Bulletin. 51(8):1235-1270. Excellent exposures of the angular unconformity at the top of the Dox Formation and the base of the Tapeats Sandstone can be seen at Mile 71.0 where Tapeats Sandstone rests on the eroded surface of the Dox Formation, and a basalt sill.
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Tedford and Barghoon recommended that the Cerro Conejo Member be reassigned to the Arroyo Ojito Formation, since there was a significant unconformity (corresponding to a hiatus in sediment deposition of 1 to 1.6 Ma) separating the Cerro Conejo from the rest of the Zia Formation. In 2007, Williams and Cole recommended that the Arroyo Ojito Formation be abandoned, because the name was being used inconsistently and because the formation straddled a significant region unconformityWilliams and Cole 2007, p.11 since named the Rincones paleosurface.Connell 2008, p.
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The Precambrian rocks were uplifted during this gap in the geologic record known as an unconformity; exposed to erosion they were gradually worn to a nearly featureless plain, perhaps resembling the vast flat areas in which similar Precambrian rocks are now exposed in central and eastern Canada. At the close of Precambrian time, about 600 million years ago, the plain slowly subsided and the site of the future Teton Range disappeared beneath shallow seas that were to wash across it intermittently for the next 500 million years.
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The Silurian, Devonian, Jurassic, and Triassic are absent in the Fort Worth Basin. From Cambrian through Mississippian time, the Fort Worth Basin area was part of a stable cratonic shelf with deposition dominated by carbonates. Ellenburger Group carbonate rocks represent a broad epeiric carbonate platform covering most of Texas and central North America during the Early Ordovician. A pronounced drop in sea level sometime between Late Ordovician and earliest Pennsylvanian time, perhaps related to the broad, mid-North American, mid- Carboniferous unconformity, resulted in prolonged platform exposure.
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Sixteen meters of deltaic sands and siltstones known as the Uzupiai Formation mark the beginning of the Cretaceous, while 53 meters of glauconite sand in the Jiesia Formation have an angular unconformity with Jurassic and Silurian rocks. A basal phosphorite layer indicates a return to deposition after a disconformity between older Cretaceous rocks and Cenomanian sequences, which also include sand, silt, chalky marl and limestone. Chalk and chert nodules are defining sedimentary features of 48 meter Turonian, 79 meter Coniacian and 40 meter Santonian age rocks.
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Continental sediments accumulated there beginning in the Eocene, formed clay, siltstone and sandstone, interbedded with thinner layers of gypsum, marl, conglomerate and limestone in river valleys formed in the central Tien Shan Mountains in the Oligocene and Miocene. These deposits range widely from several meters thick to several kilometers. They reach their greatest thickness of four kilometers in Fergana, Atbashi and Naryn basins. Tien Shan mountain rocks show no signs of folding from the Cretaceous through the Paleogene and lie with an angular unconformity atop basement rocks.
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Similar sequences are found north of the Hindu Kush and the Amu Darya Depression holds up to 10 kilometers of material from the period. Clastic sedimentation continued into the last 2.5 million years of the Quaternary. Early Pleistocene and Neogene sedimentations were often covered over coarse gravels with an angular unconformity as a result of intensive uplift in the middle Pleistocene. Glacial moraines are found above 3000 meters in the Hindu Kush and some north facing mountain slopes above 5000 meters still have glaciers.
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Coastal erosion has carved parts of the coast into sea arches, which are also of geological interest as they contain an unconformity: parts of the rocks are nearly 500 million years old, other parts are some 150 million years younger."Langness," Culture Vannin. Retrieved 17 May 2020. At the southern tip of the peninsula is Dreswick Point, the southernmost point of the Manx mainland, whilst St Michael's Isle (popularly known as Fort Island) is connected at the northern end of the peninsula by a narrow causeway.
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The unconformity is well exposed on the shores of Gairloch, Loch Maree and Loch Torridon. These rocks, which attain a considerable thickness and are divisible into three sub-groups, build up the mountain districts of Applecross, Coigach and elsewhere. Within the Torridonian tract the older Lewisian gneiss occupies large areas north of Coigach, on the east of Enard Bay, between Gruinard Bay and Loch Maree. Between the last named and Gairloch, on both sides of middle Loch Torridon and at many other spots smaller patches appear.
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4 Throughout the earlier periods of the Paleozoic, the intracratonic basin went through an extensional tectonic phase, which ended with a regional Carboniferous unconformity, representing the Hercynian orogenic compressional stage.Stewart, 2016, p.2420 From the Early Permian onwards, the basin experienced back-arc extension on the edge of Gondwana, leading to the formation of the regional Khuff Formation with anhydrite and halite deposition. This tectonic regime gradually transitioned into a passive margin setting with the opening of the Neo-Tethys in the Early Triassic.
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The town of Cleve lies on an ancient bedrock that has undergone high grade metamorphism, with the area characterised by schists, gneisses and granites in a formation known as the Hutchison Group. These strata were laid down in the Proterozoic, some 600-2300 million years ago. The area underwent deformation during the orogeny events that shaped Australia. Just south of Cleve marks an unconformity with recent Quaternary alluvial and colluvial sediments of the Piedmont Group which were deposited less than 1 million years ago.
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Sedimentary rocks deposited on top of the two microcontinents beginning in the Mesozoic. Faulting during the Triassic through the Early Cretaceous limited deposition to only a few small depressions. Sandstone, shale and conglomerate from the Triassic are found in the Ustyurt Plateau and southern Uzbekistan, containing units of bauxite deposited above an unconformity. Particularly in the Fergana Basin and the Kughitang and Zaravshansky ridges or the Gasly-Bukhara Depression, Jurassic coal and fine grained sedimentary rocks are more common, with thicknesses of 150 to 300 meters.
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The Banff Formation is overlies the Palliser Formation in the Canadian Rockies, the Wabamun Formation in central Alberta, the Exshaw Formation in southern Alberta and in the Fort Nelson area. It is overlain by the Pekisko Formation and the Livingstone Formation in north- central and southern Alberta respectively, and it is followed by the Shunda Formation in north-eastern British Columbia. An unconformity is observed between Banff and the Rundle Group in outcrop. The Banff Formation is equivalent to the Lodgepole Formation in Montana.
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The rocks were originally sedimentary until there was a collision between the North American continent and a terrane. This collision, called the Trans-Hudson Orogeny, caused the original rocks to fold and twist into a vast mountain range. Over the millions of years, these tilted rocks, which in many areas are tilted to 90 degrees or more, eroded. Today we see the evidence of this erosion in the Black Hills, where the metamorphic rocks end in an angular unconformity below the younger sedimentary layers.
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The upper Delhi Supergroup overlies on the Aravalli Supergroup with a clear unconformity. This supergroup hosts two main types of rocks: a thick sequence of volcanic rocks that is of continental affinity; and sedimentary rocks that represent fluvial and shallow marine environments and deep marine depositional environment. The depositional age of these sequences is approximately from 1.7 to 1.5 Ga. In the ‘North Delhi belt’, the Delhi Supergroup is classified into three groups: lower Raialo Group, middle Alwar Group, and upper Ajabgarh Group.Roy, A.B., Jakhar, S.R., 2002.
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The Bonneterre is overlain by of dolomite, often sandy, silty or cherty, forming the Elvins Group and the Potosi and Eminence formations. Withdrawal of the seas resulted in another unconformity during the latest Cambrian and early Ordovician periods. Hydrothermal mineralizing fluids formed the rich lead ore deposits of the Lead Belt during this time. Outcrop of Roubidoux sandstone along a bluff in Douglas County, Missouri Sedimentation resumed in the Ordovician with the deposition of the Gunter sandstone, the Gasconade dolomite and the prominent Roubidoux sandstone and dolomite.
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1981 This unit interbeds with the underlying Ojo Alamo Formation but is separated by an unconformity from the overlying San Jose Formation. The Nacimiento Formation is divided into several subunits known as members. In outcrops in southern areas of the formation, the Puercan fauna is found in the Arroyo Chijuillita Member, the Torrejonian fauna is found in the Ojo Encino Member, and the uppermost Escavada Member lacks age-diagnostic fossils. In northern outcrops, the two lower formations are indistinguishable, and are called the "main body".
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Following a sedimentary break or unconformity, the Singtali and Subathu formations were deposited as foreland basin sediments in the Garhwal Outer Lesser Himalaya during the Late Cretaceous to Middle Palaeocene. Both formations can be found overlying the Tal Formation in an extremely complex structural setting including isoclinal overturned folding and multiple thrusting events. In addition, with the similarities of the lithology as well as depositional environment, it is sometimes quite difficult to distinguish between the Singtali and Subathu Formations. The main difference discussed in the following is related to the tectonic events during their deposition.
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Although primarily exposed in the north and east, dome outcrops of basement rock exist at other locations in the country. A one billion year Proterozoic unconformity separates the basement rock from the conglomerate, quartzite, schists, iron-rich sandstones and mudstones of the Muva Supergroup. The supergroup is intruded by carbonatite, dolerite, granite, granite porphyry, lamprophyre, norite, pegmatite and other igneous rock types. A rhyolite porphyritic belt, formed at the same time as the Muva Supergroup extends along the eastern bank of the Luapula River, between Lake Tanganyika and Lake Mweru.
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Metamorphic rocks are exposed near Stromness and Yesnaby on Mainland and on Graemsay.Basement geology of Orkney, Hall, Adrian and Brown, John, "Orkney Landscapes" (online) (Edinburgh, Scotland) September 2005, Last update 10-Nov-2008 Most of the basement consists of granitic gneisses and later minor intrusions. These rocks are similar to those seen in northern Caithness and have been correlated with the Loch Eil Group of the late Proterozoic Moine sequence. The unconformity at the base of the overlying Devonian rocks is highly irregular, with the exposed basement forming hills in this buried land surface.
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Water flowed eastward into Lake Stanley from Lake Chippewa through the Mackinac Channel. Lake Stanley, also called the Stanley unconformity, is a postglacial freshwater lake that occupied part of what is now the basin of Lake Huron during a hydrologically significant period from 10,000 years Before Present (B.P.). The lake’s surface level was approximately 70 meters below the current lake’s water surface. The lake, although geographically smaller than the current Lake Huron, was fed from a large Lake Chippewa watershed that included the basin of what is now Lake Michigan.
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At this location, it consists of a thin layer of highly ferruginous sandstone that is composed of sediments derived from the underlying Cardenas Basalt and a 10 m thick ferruginous weathered zone (paleosol) developed in the eroded surface of the Cardenas Basalt.Elston, DP, and GR Scott (1976) Unconformity at the Cardenas-Nankoweap contact (Precambrian), Grand Canyon Supergroup, northern Arizona. Geological Society of America Bulletin. v. 87(12):1763-1772 The upper member of the Nankoweap Formation consists of about 100 m of generally reddish-purple, fine-grained, quartzitic sandstones.
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Associated with this thickening is a stratigraphic range from coarser, lower to middle-Jurassic sedimentary units to upper-Jurassic shale, which marks the Husky formation. The Husky formation is one of the two shale units in the Aklavik range, and is characterized by its fossil assemblages. The “Husky shale” lies immediately above the bivalve rich, heavily bioturbated Aklavik sandstone. The “Husky shale” is one of the youngest units (second youngest to the Porcupine River formation) in this wedge-succession and marks an unconformity with the Aklavic sandstone units below.
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Deposition of the Pinguicla group began at 1.38 Ga after a significant period of weathering. Deposition of these sediments indicates a period of rifting and extension in the area, as supported by the incidence of the Hart River volcanic at the same time period. The period of rifting and crustal extension embodied by the Hart River volcanics was followed by basin sedimentation represented by the Pinguicula group. The Pinguicula group is separated from the Wernecke Supergroup by an angular unconformity, representing an erosional stage after the Racklan orogenic event.
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In the Late Eocene, above the Rajang Group, there is a period of no deposition, marking the tectonic uplift event of the Sarawak Orogeny. This period of time with no deposition is called an unconformity and appears as a gap in time in the sedimentary record. Following this, Oligocene deposition of the Kinabatangan Group occurred, which also consisted of turbidites and marine mudstones. Turbidites and mudstones are indicative of a deep marine environment due to the low energy in deep oceans which forms the fine grained mudstones with occasional submarine landslide type events forming turbidites.
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An unconformity separates the Curaçao Lava Formation from the Knip Group, which includes the Zevenbergen limestone and Casabao limestone laden with fossilized foraminifera, crinoids, rudists, corals and gastropods from the Late Cretaceous. The formation is two kilometers thick in the west but only 100 meters thick in the southeast. In the northwest, mudstones, breccia and boulder beds in the Knip Group grade into the Seroe Gracia Formation, which has 300 meters of chert limestone. This formation is overlain by 750 meters of sandstone, siltstone, mudstone and marl in the Lagoen Formation.
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A sequence of Cambrian to Lower Ordovician sediments of the Eriboll and Durness Groups lie above the Torridonian with an angular unconformity. The Lower Cambrian Eriboll Group comprises a basal quartzite, locally with a basal conglomerate, followed by the distinctive Pipe Rock Member, a quartz arenite with white weathering skolithos trace fossils. The Pipe Rock is overlain by the Salterella Grit, a coarse sandstone, and the Fucoid Beds, a sequence of calcareous sandstone and siltstone. The overlying Durness Group comprises a series of dolomites of Upper Cambrian to Middle Ordovician in age.
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The Acadian Foreland Basin is a Retroarc Foreland Basin Foreland basins are a product of tectonic deformational loading, or crustal thickening along the orogen, a consequence of overthrusting and folding. The Acadian foreland basin is categorized as a retroarc foreland basin, which occurs on the overriding continental lithosphere, adjacent to a foreland fold-thrust belt behind a continental margin arc. The initial result of loading is a bulge move out and uplift of the foreland, which generates a localized unconformity. The distributions of unconformities display an asymmetric pattern in relation to the promontories.
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Middle Cambrian is characterized by uplift and regression; however, a renewed progression at this time led to the deposition of Mila and Kuhbonan Formations, consisting of limestone, dolomite, and shale, over older units. These formations bear trilobites and brachiopods of Middle and Late Cambrian age. In some areas, the Late Cambrian carbonate facies turns transitionally into Ordovician graptolite shales, known as the Lashkarak Formation in Alborz, Shirgasht Formation in Central Iran and Ilbeyk and Zardkuh Formations in Zagros. In Kalmard area, Ordovician sediments are sitting on the Vendian sediments through an angular unconformity.
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The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much thinner. The Dockum rests on an unconformity over the Anisian (242–234 Ma) aged Anton Chico Formation. The Dockum and Chinle Formation were deposited roughly at the same time and share many of the same vertebrates and plant fossils.
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Another view of the Natural arch In the 1980s, during excavations for a geological fault in the Tirumala hills, geologists found this rare geological formation of the rock arch which has two dissimilar sets of rocks with a connecting thin link. The assessed geological age of the rock arch is 2.5 million years. Formation of the arch is attributed to intensified weathering and erosion of stream action that has withstood the torque of nature. This is a rare geological fault which is technically called in the geological idiom as ‘Eparchaean Unconformity’.
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Missoula: Mountain Press Publishing Co., 1991. p. 381 Most of the strata visible in the canyon were deposited during the Permian and Triassic periods. From oldest to youngest, and each separated by an unconformity, the formations are: The Quartermaster Formation is Permian in age, and forms the red, lower slopes of the Canyon. This layer was deposited in a near-shore shallow-marine environment consisting of siltstones and shales with ripple marks and cross bedding, that alternated with dry tidal flats indicated by satin spar gypsum and halite cast evaporite deposits.
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120-1 The source rock for the South Cuyama oil is most likely the Soda Lake Shale member of the Vaqueros Formation.Provenance of oil in southern Cuyama basin, California (Abstract of a paper presented at a conference of the American Association of Petroleum Geologists) Overlying the faulted and broken Miocene rocks, which include the Monterey, Branch Canyon, and Santa Margarita Formations, and separated by an unconformity, is about 2,000 to of the Pliocene Morales Formation. None of these upper rocks are oil-bearing, although gas has been produced from the Santa Margarita Formation.DOGGR, p.
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The McMurray Formation is conformably overlain by the Wabiskaw Member of the Clearwater Formation. It is underlain by Devonian formations that were tilted and eroded prior to the deposition of the McMurray, resulting in a shallow angular unconformity between the McMurray and the underlying units. The McMurray therefore rests on different Devonian units in different parts of the basin. These range from the Elk Point Group in the east near the Saskatchewan border, to the Waterways Formation along the Athabasca River, and the Banff, Wabamun, and Winterburn Formations farther west.
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It represents the remnants of a much higher range of hills that existed hundreds of millions years ago. This has allowed the formation of features such as Cheddar Gorge, Ebbor Gorge and Burrington Combe. There are a wide variety of caves and swallet holes caused by dissolution of the rock by water. Further east there are Silurian volcanoes, Carboniferous Limestone outcrops, Variscan thrust tectonics, Permo-Triassic conglomerates, sediment-filled fissures, a classic unconformity, Jurassic clays and limestones, Cretaceous Greensand and chalk topped with Tertiary remnants including Sarsen Stones.
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In Northern Hainan, there is a prominent fault, the Changjiang-Qionghai fault, along which shows the traces where the oceanic basin rifted apart under consistent extension in Late Paleozoic. The Cambrian and Permian units were then deposited in the basin. Also, it is suggested that from the Late Devonian to Permian, Hainan Island as part of the South China Block drifted towards the Southeast Asian crustal plate in the north, breaking away from the East Gondwana. As a result, there was an unconformity between the Paleozoic and the Mesozoic units.
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The youngest bone remains in the cave date to 60,000 years ago, and the youngest stone tools to 50,000 years ago. The previous estimate of 12,000 BCE was due to an undetected unconformity in the cave stratigraphy. Their disappearance is close to the time that modern humans reached the area, suggesting that the initial encounter caused or contributed to their extinction. This would be consistent with the disappearance of H. neanderthalensis from Europe about 40,000 years ago, within 5,000 years after the arrival of modern humans there, and other anthropogenic extinctions.
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There is a gap of about a billion years between the 500-million-year-old stratum and the level below it, which dates to about 1.5 billion years ago. This large unconformity indicates a long period for which no deposits are present. Many of the formations were deposited in warm shallow seas, near-shore environments (such as beaches), and swamps as the seashore repeatedly advanced and retreated over the edge of a proto-North America. Major exceptions include the Permian Coconino Sandstone, which contains abundant geological evidence of aeolian sand dune deposition.
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At the time of sedimentary deposition, the Karoo retroarc foreland system was in an overfilled phase, and purely terrestrial sediments occupied the Karoo Basin at this time. Two fining-upward sequences are observed in the sedimentary stratigraphy of Daptocephalus biozone, bounded by a second-order subaerial unconformity. These sedimentary rocks comprise greenish-grey mudrock with siltstone lenses in the lower to middle sections of the biozone, which are indicative of a low-energy fluvial environments with meandering rivers. It is in these rocks that fossils are most commonly found.
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Vallis Vale () is a 23.9 hectare biological and geological Site of Special Scientific Interest near Great Elm in Somerset, notified in 1952. Vallis Vale is an ancient woodland site and supports an Ash-Wych Elm stand type with a restricted distribution in Britain. Vallis Vale exposes some of Britain's most classic rock outcrops, exhibiting several of the most easily demonstrated examples of angular unconformity available. A nationally important research and educational locality, of great renown for the part it has played in the historical development of geological science.
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It is visible from Route 21 north of Centerville and from Route N approaching Johnson's Shut-ins State Park from the south. Before the failure of the upper reservoir, visitors could drive to the top of Proffit Mountain and walk to an observation deck above the reservoir. Ameren operated a museum at the entrance gate highlighting the geologic and natural history of Missouri. The power plant was frequently visited by geology students because of a striking example of Precambrian/Cambrian unconformity in the rock layers exposed by the plant's construction.
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Slope development will periodically undermine the formations above and car- to house-sized blocks of that rock will cascade down onto the Tonto Platform. An unconformity marks the top of this formation . Lizard-like animals left their footprints in Coconino Sandstone Coconino Sandstone formed about 275 million years ago as the area dried out and sand dunes made of quartz sand invaded a growing desert (see 6b in figure 1). Some Coconino fills deep mudcracks in the underlying Hermit Shale and the desert that created the Coconino lasted for 5 to 10 million years.
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479-80 There were also intervals where black shale accumulated in abundance on the continents, indicative of a stagnant water column; apparently water in the polar oceans was too warm to sink and oxygenate the deep-sea, as it does today.Stanley, p. 480 Many of these black shales are now rich in petroleum sources. The waters of the Zuñi sequence began to subside late in the Cretaceous period, and by the early Cenozoic a new craton-wide unconformity in North America indicates a complete regression before the Tejas sequence of the late Paleogene.
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Formation of the Taranaki Basin initiated in the Late Cretaceous, due to the separation of Australia and Zealandia during the breakup of Gondwanaland. This breakup caused the formation of the Tasman Sea, along with multiple extensional basins on the New Zealand subcontinent, including an intra-plate rift that formed the Taranaki Rift, which would develop into the Taranaki Basin. Syn-rift sediments were deposited within rift controlled grabens across the basin, and are separated from the basement rock by a regional unconformity. These sedimentary layers contain faulting that is indicative of extension during deposition.
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Typically, the surface of this unconformity is a remarkably flat, ancient erosional surface, often argued to be a peneplain, that cuts across units such as the Bass Formation, Hatakai Shale, and Dox Sandstone. Resistant beds within the Unkar Group, such as Cardenas Basalt and Shinumo Quartzite, form ancient hills, called monadnocks, that rise as much as high above this ancient plain. Thin drapes of Tapeats Sandstone of the Tonto Group now cover most of these ancient monadnocks. However, a few of these monadnocks protrude up into the Bright Angel Shale.
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In 1787, the geologist James Hutton noted what is now known as the Hutton Unconformity at Inchbonny, near Jedburgh. Layers of sedimentary rock which are tilted almost vertically are covered by newer horizontal layers of red sandstone. This was one of the findings that led him to develop his concept of an immensely long geologic time scale with "no vestige of a beginning, no prospect of an end." The Scots name for the town is part of the expression "Jeddart justice" or "Jethart Justice", in which a man was hanged first, and tried afterwards.
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Examples of this type of architecture are illustrated in the main rift units of Statfjord North and Gyda Fields. The Visund fault block and the Oseberg-Brage infill are examples from marine half-grabens which are near the central or axial zones of the northern North Sea rift complex, far from the main hinterland areas and show deepening upward trends into basinal shales. The syn-rift unconformity describes the erosion surface that bevels fault blocks during continental rifting. It develops locally over individual fault blocks because of footwall uplift and lithospheric unloading by extension.
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In the 18th century, finds such as Hutton's Unconformity showing layers tilted, eroded, and overlaid, demonstrated the "abyss of time" in the geologic time scale. Modern geology, its sub-disciplines and other scientific disciplines utilize the scientific method to analyze the geology of the earth. The key tenets of flood geology are refuted by scientific analysis and do not have any standing in the scientific community. Modern geology relies on a number of established principles, one of the most important of which is Charles Lyell's principle of uniformitarianism.
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This sea-level drop and the associated unconformity in North America separate the Mississippian Period from the Pennsylvanian period. The Carboniferous was a time of active mountain building, as the supercontinent Pangea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America-Europe (Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly uplifted Appalachians southwestward as the Ouachita Mountains.
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During the Middle-Late Jurassic, the center of the North Sea underwent a doming acknowledged by the Middle Jurassic erosional unconformity, the erosion of > of Upper Triassic and Lower Jurassic strata. The dome raised above sea level during the Middle Jurassic and began to deflate due to rifting in the Late Jurassic. Though the mechanism forming the North Sea Rift Dome is not particularly well understood, the development of the dome seems to be consistent with an active rift model having a broad-based ( diameter) plume head influencing the Late Jurassic rifting.
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This embayment, called the Amargosa aulacogen, had highlands north and south of it and was the result of a failed rift. Many thousands of feet of sediment filled the slowly subsiding basin. Next, the metamorphosed Precambrian basement rocks were uplifted and a nearly 500-million-year-long gap in the geologic record, a major unconformity, affected the region. Geologists do not know what happened to the eroded sediment that must have overlain the complex, but they do know that regional uplift was responsible; the area was originally below the surface of a shallow sea.
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Cliff at the east of Siccar Point showing the unconformity between red sandstone and greywacke. Siccar Point: eroded sandstone outcrop above conglomerate and vertical ribs of greywacke, a feature sketched in 1788 by Sir James Hall. In the spring of 1788 Hutton set off with John Playfair to the Berwickshire coast and found more examples of this sequence in the valleys of the Tour and Pease Burns near Cockburnspath. They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass.
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The Union Springs is an organic-rich, pyritiferous, thinly bedded, blackish gray to black shale with mudstone concretionary layers, and thin silt bands at the bottom. To the east, it becomes the Bakoven Member, a darker, less organic shale with fewer limestone layers. To the west the Union Springs beds thin, with its upper limestones merging with the overlying calcareous Cherry Valley Member. A regional unconformity appears in western New York, as the Union Springs lenses in and out, and then reappears in northwest Pennsylvania and northeast Ohio between the Onondaga and Cherry Valley.
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It lies transitionally above the Jagüel Formation, and the top of the formation is marked by a regional unconformity due to an Eocene and Oligocene orogenic pulse. These two units belong to the Malargüe Group. The marine sediments of the Jagüel and Roca Formations were deposited during a transgression from the Atlantic Ocean, beginning in the Maastrichtian and ending in the Danian. Lime kiln in Barda Norte Locality, General Roca, Río Negro, Argentina The stratotype of the Roca Formation is located north of General Roca, Río Negro (39º40´S, 67º32´W).
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The Kaskaskia sequence was a cratonic sequence that began in the mid-Devonian, peaked early in the Mississippian, and ended by mid-Mississippian time. A major unconformity separates it from the lower Tippecanoe sequence. The basal—that is, the lowest and oldest—units of the Kaskaskia consist of clean quartz sandstones eroded from the Appalachian orogenic belt to the east, the Ozark Dome in the center of the continent, and south from the Canadian Shield. These sandstones are followed by extensive carbonates, though these are often difficult to distinguish from preceding Tippecanoe carbonates.
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Late Triassic (220 Ma) The sediments of the Caturrita Formation belong to the second unit of the Santa Maria Supersequence and overlie the Alemoa Member of the Santa Maria Formation. The clayey sediments of the Alemoa Member gradually give way to the more sandy, rarely conglomeratic, Caturrita Formation, which finishes with an unconformity. After this erosional event follow the Rhaetian sediments of the Mata Sandstone, the third unit of the Santa Maria Supersequence. The Caturrita Formation was once regarded as a member of the stratigraphically higher Botucatu FormationBortoluzzi, C.A. 1974.
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A three-stage model of evolution has been proposed for the Arauco Basin. First a phase of extension in the Late Cretaceous and Paleogene. Then a basin inversion lasting from the Middle Eocene to the Miocene causing the uplift and erosion that created the “main unconformity” and finally a post-inversion phase of strike-slip faulting in the Pliocene and Pleistocene. The subduction of the Mocha Fracture Zone under the basin that begun about 3.6 million years ago is believed to have caused the uplift of the basin plus some further tectonic inversion and contraction.
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The project used airborne geophysics and on-ground investigations and was funded by the National Science Foundation and the Moore Foundation. Along with her work in Antarctica, Siddoway has pursued research in the Front Range of the Colorado Rocky Mountains. This work led to a surprising result for the age of Cryogenian sandstone dikes within granite host rock, a matter that had been unresolved for more than 125 years. The Tavakaiv quartzite formation contributes to new appreciation of the time of formation of The Great Unconformity in Colorado.
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American Association of Petroleum Geologists bulletin, 86 (7), 1305-1328 The Zonguldak basin was tectonically active during the late Paleozoic and this strongly influenced its structural and burial history due to the Hercynian orogeny. The Hercynian orogeny was the result of the continent–continent collision between Laurasia and Gondwana. This collision created many E-NE/W-SW striking faults, folds, and tilted the Paleozoic sediments. This uplift of the basin, near the end of the Westphalian, halted deposition and created the angular unconformity at the top of the Karadon Formation.
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This would indicated that Paleozoic strata that covered much of Fennoscandia elsewhere had been locally uplifted and eroded prior to the formation of the Sub-Mesozoic hilly relief. The Sub-Mesozoic hilly peneplains covers a contiguous zone along western and southern rims of the South Swedish Dome. This zone includes most of Bohuslän, Halland and Blekinge as well as parts of Västergötland and Scania. In parts this surface and unconformity makes up an undullating hilly relief, while in other locations like Blekinge and northern Halland it is an joint valley landscape.
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Most rocks that outcrop on the surface on Bahrain Island and the Huwar Islands date to the Eocene in the Cenozoic. The rimrock of Eocene limestone forms a ring around the main island, with cliffs up to 30.5 meters (100 feet) tall and wind erosion features are common. An angular unconformity separates middle Eocene rocks from sandier Miocene rocks. The Rus Formation is 56.1 meters thick, encompassing the Ad Damman area in Saudi Arabia and is exposed in central Bahrain as limestone with chert and chalk layers along with quartz geodes.
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The Neoarchean supracrustal sequence known as the Central Slave Cover Group (informally Dwyer Group) is a 2.9–2.8 Ga package of fuchsitic quartzites overlain by banded iron formations. This fuchisitic quartziite sequence seems to be characteristic of many other cratons between about 3.1 and 2.8 Ga and marks a global peak in quartzite production. The Central Slave Cover Group is typically 100 to 200 meters thick. A quartz pebble conglomerate found at the base of the Central Slave Cover Group marks a distinct unconformity that is laterally continuous over much of the CSBC.
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Within the Grand Canyon region, the Kaibab Limestone overlies gypsum and contorted sandstones of the Toroweap Formation. Originally, geologists interpreted the lower contact of the Kaibab Limestone to be an unconformity based on the presence of local intraformational breccias and erosional surfaces. However, additional research has concluded that these local intraformational breccias and erosional surfaces are the result of collapse following the dissolution of evaporite deposits within the upper part of the Toroweap Formation. As a result, this contact is inferred to be conformable or only locally a disconformity.
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The unconformity and disconformity are inferred to represent most of Permian time (including the Leonardian) and part of Early Triassic time. Although the Moenkopi Formation overlies the Kaibab Limestone, its redbeds have been removed almost entirely by erosion because they are less resistant to erosion than the strata of the Kaibab Formation. As a result, the Kaibab Limestone forms the surface of many of the vast plateaus that border the Grand Canyon. Within these plateaus, the uppermost beds of the Kaibab Limestone have also been largely removed by erosion.
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Underneath them is the relatively impermeable Sisquoc Formation, of Pliocene and Miocene age. Beneath this unit, and separated by an unconformity, is the oil-bearing rock, the fractured shale of the Miocene-age Monterey Formation, at the top of which oil has pooled, halted in its upward migration by the impermeable cap of the Sisquoc. The minimum depth at which oil has been recovered in the Lompoc field is approximately , and the average net thickness of the oil-bearing rock is 450 to . Total productive area of the field is .
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The Athabasca basin, a historical fluvial siliciclastic basin with sediments from the Hudsonian mountains with the occasional rare marine sequence. The Athabasca basin was formed during the Statherian or Paleohelikian 1.7 to 1.6 billion years ago when coarse fluvial and marine clastic sediments were laid down containing gold, copper, lead, zinc, and uranium oxides. The highest grade uranium deposits in the world are found at the unconformity between these clastic layers and the Precambrian bedrock. The Athabasca Sand Hills protected by The Athabasca Sand Dunes Provincial Park are unique feature of the Canadian Shield.
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366-369 The capping geologic units are the Sisquoc, Careaga, and Foxen formations. The Careaga and Foxen are of Pliocene age, while the thicker, diatomaceous Sisquoc is both Pliocene and Upper Miocene. Beneath these, separated by an unconformity, is the fractured shale of the Monterey Formation which has been richly productive for over 100 years. This is the same producing formation as in many other California oil fields, including the Lompoc Oil Field in the similarly anticlinal ridge of the Purisima Hills to the south, and the Zaca field to the southeast.
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For example, lackwelderia tenuilimbata (a type of trilobite) zone in Gushan formation. The trilobite biozones can be useful to correlate and identify events in different places, like identifying unconformity sequences from a missing biozones or correlates events happening in a neighbouring block (like Tarim block). The carbonate sequence can also be of evolutionary significance because it indicates extinction events like the biomeres in the Cambrian. Biomeres are small extinction events defined by the migration of a group of trilobite, family Olenidae, which had lived in deep sea environment.
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The issue was finally resolved by GreenJ. F. N. Green On the Geological Structure of the St David’s area, Pembrokeshire., 1908, Journal of the Geological Society of London. 64 363-383 by revealing, in an excavation, an unconformity in which an excavation of a Cambrian basal conglomerate is shown to cut the granophyre.P. J. Brenchley, P. F. Rawson The Geology of England and Wales, 2006, 2nd EdJ. F. N. Green On the Geological Structure of the St David’s area, Pembrokeshire., 1908, Journal of the Geological Society of London.
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The formation is made up of the Kicking Horse member, which includes the Alalcomenaeus-Sanctacaris beds; this underlies and interdigitates with the unfossiliferous Yoho River member. These two are truncated by an unconformity and covered by the Campsite Cliff member, which contains the Ogygopsis beds. The Wash member, which contains many shelly but no soft-bodied fossils, interrupts this sequence in places, and directly underlies the Phyllopod beds, which mark the base of the Walcott Quarry member. This underlies the Wapta member, which is unconformably overlain by 'Tokumm'.
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The mine was closed by the 11th Duke of Hamilton on the grounds that it "spoiled the solemn grandeur of the scene" but was reopened after the First World War and operated until 1938 when the vein ran out.Hall (2001) p. 28 Visiting in 1787, the geologist James Hutton found his first example of an unconformity to the north of Newton Point near Lochranza, which provided evidence for his Plutonist theories of uniformitarianism and about the age of the Earth. This spot is one of the most famous places in the study of geology.
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Gurney Slade quarry Gurney Slade quarry, is a limestone quarry near Gurney Slade between Binegar and Holcombe, on the Mendip Hills, Somerset, England. Gurney Slade quarry exhibits pale to very dark grey Carboniferous Limestone overlain by red and purple-coloured Triassic breccias and marls with a small faulted block of overlying Lower Jurassic breccias forming an angular unconformity with the Carboniferous Limestone. There is abundant vertical sediment infilled fissures and joints (Neptunian Dykes). The rocks contain varying amounts of calcite mineralization, and there is common fossil material associated with the Carboniferous and Jurassic limestones.
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The Hematite Creek Group was deposited in the middle Proterozoic, 1.0 Ga - 1.1 Ga. This group is delineated from the Pinguicla Group by a 300 million year gap in the sediment record and an unconformity type boundary. The Hematite Creek Group is approximately a kilometer thick and is composed mostly of clastic and carbonate sediments. These sediments were deposited in a shallow ocean environment, as evidenced by preserved stromatolites, mud cracks and interference ripples. Sediment supply for the Hematite Creek basin formation has been tentatively attributed to the Grenville orogeny of approximately the same time period through U-Pb dating of zircon grains.
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The Burgersdorp Formation is the top unit of the Beaufort Group and the oldest Karoo-related unit in Lesotho, with red and maroon sandstones interspersed with thin coal seams. The Stormberg Group is divided between the Molteno Formation, Elliot Formation and Clarens Formation. The Molteno Formation is 15 to 300 meters thick and records a Late Triassic lake bed environment, with abundant plant and insect fossils. There is an unconformity between the Molteno and the overlying 70 to 250 meter thick sandstones, mudstones and siltstones of the Elliot Formation, which contains silicified wood and dinosaur fossils.
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The Carapacha Formation is a geological formation of the Sierra de Calencó, Carapacha Basin of La Pampa Province, Argentina whose strata date back to the Artinskian to Wuchiapingian of the Permian. The formation comprises two members, the lower Calencó member, named after the eponymous mountain range, and the Urre-Lauquen member, named after the Urre-Lauquen Lake bordering the range to the north. The members are separated by an unconformity and represent a lacustrine (Calencó) and fluvial-dominated depositional environment. Ichnofossils of several groups of Permian reptiles and amphibians as well as flora have been retrieved from the formation.
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Nepheline syenites are rare; there is only one occurrence in Great Britain (Loch Borralan)Sutherland, D.S. (editor) (1982) Igneous Rocks of the British Isles, page 211 and one in France and Portugal. They are known also in Bohemia and in several places in Norway, Sweden and Finland. In the Americas these rocks have been found in Texas, Arkansas, New Jersey (Beemerville ComplexEby, G. N., 2012, The Beemerville alkaline complex, northern New Jersey, in Harper, J. A., ed., Journey along the Taconic unconformity, northeastern Pennsylvania, New Jersey, and southeastern New York: Guidebook, 77th Annual Field Conference of Pennsylvania Geologists, Shawnee on Delaware, PA, p.
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View of the bay from Culver Down Whitecliff Bay has nearly identical geology to the lesser known Alum Bay, being a coastal section of the same strata which run east-west across the island. It displays a classic sequence of fossil-bearing Eocene beds of soft sands and clays, separated by an unconformity from the underlying Cretaceous Chalk Formation forming the headland of Culver Down to its south. Due to geological folding of the Alpine orogeny, the strata in the main section of the Bay are vertical, with younger rocks to the north.West, Ian M. 2007.
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Stratigraphic column of the formation The formation comprises a sequence of rhythmically alternating shales and red sandstones with a minimum thickness of . The lower part of the formation was deposited under marine conditions and the upper part in a meandering river floodplain and point bar environment. Paleocurrent analysis demonstrated a flow direction towards the west, northwest and west- northwest. The formation contains ichnofossils of theropods and ornithopods, occurring in the Early Cretaceous upper part of the formation, which is marked by an angular unconformity, overlain by volcanic and clastic rocks of the Late Cretaceous to Early Paleocene Cerro Empexa Formation.
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The overlying Paleozoic quartzite and limestones rock lies on an unconformity with a total thickness ranging from , and contains of Mississippian Escabrosa Limestone and the Naco Formation limestone of Pennsylvanian age in the upper formations. Overlying the Naco Limestone is an unconformable Mesozoic series of conglomerate, thick-bedded quartzites, and shales, with two or three lenses of soft, bluish-gray limestone. Into these formations intrude intruded great bodies of quartz monzonite and by dikes of quartz monzonite-porphyry and diorite-porphyry. Structural faulting occurs throughout the district especially immediately south of Tombstone, where the strata are closely folded.
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Several of these dikes are exposed around the swinging bridge and also just outside the park where Highway 210 crosses the river below the Thomson Dam. They are nearly the same color as the Thomson slate, but can be distinguished by their horizontal columnar joints and lack of slaty cleavage. Around Jay Cooke State Park, the basalt from the Midcontinent Rift eruptions eroded away long ago. In fact the rock layer immediately above the Thomson Formation is the Fond du Lac Formation, which dates from the late Mesoproterozoic era, an unconformity of about 800 million years.
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California geology and tectonics — Luyendyk moved to UCSB in 1973, where he began research in southern California tectonics using paleomagnetism. His projects include documenting the ninety degree or greater clockwise rotation of the Transverse Ranges during the Neogene Period of the Cenozoic Era. Drilling into Deep Ocean Floor — Luyendyk led two expeditions of the Deep Sea Drilling Project. Principal discoveries included that of a basin- wide unconformity of Oligocene age in the Indian Ocean that was likely related to initiation of ice sheets in Antarctica and uplift of the Reykjanes Ridge due to the Iceland hot spot.
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The oldest stage of activity is known as Vinta Loma and formed the bulk of the volcanic edifice, especially on the eastern side and in the summit area. During this stage, lava flows and some pyroclastic flows were erupted from a central vent. The pyroclastic flows are exposed as a thick sequence in a cirque close to the summit and reflect the occurrence of Plinian eruptions during this stage of volcanic activity. The Vinta Loma series is subdivided into two groups separated by an unconformity, which are dated to 870,000 ± 80,000–641,000 ± 9,000 and 910,000 ± 170,000–1,230,000 ± 80,000 years ago respectively.
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This lag layer overlies an unconformity eroded into older glacial till, lake sediment, or bedrock. This surface extends from the lower reaches of the Kettle River valley as far south as Sunrise, Minnesota. The Chengwatana surface likely was cut by water flowing down the Kettle River from the Moose Lake outlet of glacial Lake Nemadji and the Epi- Duluth level of glacial Lake Duluth. The association of the Chengwatana surface with glacial Lake Nemadji and the Epi-Duluth level of glacial Lake Duluth would make it most likely range in age from before 12,100 to about 11,700 BP calibrated.
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Newmont discovered the world's first submicroscopic or "invisible" gold at Carlin, Nevada in the early 1960s and began production on the first open pit gold mine in the world. The "Carlin Trend" or "Carlin Unconformity" is the largest gold discovery in North America during the 20th century. In 1971 Newmont began using the heap leaching technology on sub-mill grade ores there. In the 1980s, Newmont thwarted five takeover bids – from Consolidated Gold Fields (ConsGold), T. Boone Pickens, Minorco, Hanson Industries and Sir James Goldsmith – who sought to break Newmont apart and sell its assets to increase shareholder value.
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The Mackenzie Mountains Supergroup in the east and the Fifteenmile Group in the west deposited with carbonates, sandstone, siltstone and shale around one billion years ago. Regional folding, which produced the Corn Creek orogeny took place around 900 million years ago, leaving behind interlaced transcurrent faults in the vicinity of the current day Snake River. This interpretation is supported by a low angle unconformity underneath the Callison Lake Dolomite in the south of the Ogilvie Mountains. The Yukon was part of the supercontinent Rodinia until began to break up 850 million years ago, separating the proto-North American continent of Laurentia.
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Skirwith Cave is a solutional cave formed in the lowest beds of the Visean Great Scar limestone from the Mississippian Series of the Carboniferous period, which here lies unconformably on impervious Ordovician rocks. The cave runs up dip NNE towards the valley of Crina Bottom, and drains the area around Boggarts Roaring Holes on the other side of the valley, although in times of flood it also takes water from overflow sinks in Crina Bottom itself. A fragment of the continuing passage has been entered from Lower Hardgill Pot, some away in Crina Bottom. The water resurges on the basal unconformity.
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Since the Miocene (23.03 – 5.333 million years ago), sedimentation rates appear to have decreased as the guyot moved away from waters with high biological productivity and at some point in the last 10 million years erosion increased due to bottom currents linked to the glaciation of Antarctica. Pelagic sediments accumulate on some guyots after they have drowned. A dome- shaped cap of pelagic ooze accumulated on top of Horizon Guyot during the Tertiary, reaching a maximum thickness of - in some places. In the saddle between the summit platforms it is about thick; an unconformity separates it from Cretaceous deposits.
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The breakup of Rodinia one of the oldest supercontinents, produced rifts between 900 million and 600 million years ago in the Neoproterozoic. These deep extensional basement faults filled with sediments, such as the Uinta rift basin and were often reactivated more recently in Earth history by orogenies. The Uinta Formation and Uncompahgre Formation are both examples of remnant Precambrian rift basin sediments. The end of the Neoproterozoic is not known from the rock record, indicating a period of long-running terrestrial erosion which produced by the Great Unconformity, from 1.1 billion to 510 million years ago.
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Most Carolina bays consist of a few meters of sand and (or) mud that rest on a unconformity above a harder substrate that does not show signs of deformation or other disturbance. The composition and the age of this harder substrate varies from location to location. Furthermore, stratigraphic relations of some Carolina bays with fields of eolian dunes in river valleys suggest that Carolina bays formed episodically during different times at different places. For example: :In some places, Carolina bays are inset into fields of eolian dunes in river valleys, and thus these Carolina bays must be younger than the underlying eolian dunes.
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The syn-rift unconformity separates the rift from the following post-rift stage and, with the exception of faulted terrain, it is the most pronounced feature of rift basins. A northern North Sea example is in the Snorre Field where its crestal part was exposed to subaerial and subaqueous erosion during much of the late Jurassic and as much as 1 km of sediments has been removed in the northern part of the block. Other fault blocks in the North Sea, such as the Oseberg fault block, have rounded or flat tops resulting from erosion and peneplanation down to sea level.
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From oldest to youngest they comprise the Llandovery age Reservoir Formation (named for North Esk Reservoir where these rocks are to be found), the Deerhope Formation, the Cock Rig Formation and the Wether Law Linn Formation overlain by the Wenlockian age Henshaw Formation. These are in turn unconformably overlain by the late Silurian to early Devonian age sandstones and conglomerates of the Greywacke Conglomerate and Swanshaw Sandstone formations. A further unconformity separates these from the overlying Pentland Hills Volcanic Formation though all three formations are collected together within the Lanark Group. The Volcanic Formation forms such summits as East and West Kip.
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The Cape granites were emplaced and the Kaaimans Group rocks were folded and thermally metamorphosed during this period. The formation of the main basin in the Cape Province commenced 570 Mya and lasted for 200 My. The Table Mountain Group is thick and an erosional unconformity marking its base is composed of both terrestrial and marine sediments. Synclines along the coast of the southern Cape contains sediments from the Bokkveld Group. The Cape Fold Belt (CFB) rocks and the Karoo Basin were deposited 450 Mya; the Cape Supergroup 450-300 Mya during a series of transgression-regression cycles.
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A long period of uplift and erosion was concurrent with and followed the above events, creating a major unconformity. Sediments worn off the Death Valley region were shed both east and west and carried by wind and water; the eastern sediments ended up in Colorado and are now famous for their dinosaur fossils. No Jurassic to Eocene sedimentary formations exist in the area except for some possibly Jurassic-age volcanic rock around Butte Valley. Large parts of previously deposited formations were removed; probably by streams that washed the sediment into the Cretaceous Seaway that longitudinally divided North America to the east.
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Carboniferous deepwater limestone forms a four kilometer flysch in the Cis- Urals Foredeep Basin in the South Urals region, which also includes olistrosomes and a Permian salt-bearing marine molasse. Middle Cambrian rocks in the Kazakh Uplands have an angular unconformity with older rocks because they were thrust onto a magmatic arc in the Devonian to the northwest of the Karaganda Foredeep Basin. Within the foredeep basin, limestone deposition shifted to coal-bearing molasse. Small synclines in the Karaganda Foredeep Basin show deepwater limestone and shale 450 meters thick from the Carboniferous and Permian, as well as 4.5 kilometer thick coal-bearing molasse.
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In December 2004, the Cigar Lake Joint Venture (AREVA Resources Canada 37.1%, Cameco Corporation 50.025%, Idemitsu Uranium Exploration Canada Ltd. 7.875%, and TEPCO Resources 5%) partners agreed to proceed with development of the Cigar Lake uranium mine -the second largest known high-grade uranium deposit in the world, after McArthur River. With federal and provincial approvals in place, full construction began in January 2005. All of Canada's uranium production now comes from the high-grade unconformity-type uranium deposits of the Athabasca Basin of northern Saskatchewan, such as Rabbit Lake, McClean Lake, McArthur River, and Cigar Lake.
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Early Jurassic uplift created an unconformity above the Chinle Formation that represents about ten million years of missing sedimentation between it and the next formation, the Moenave. Periodic incursions of shallow seas from the north during the Jurassic flooded parts of Wyoming, Montana, and a northeast–southwest trending trough on the Utah/Idaho border. The Moenave was deposited in a variety of river, lake, and flood-plain environments. Moenave Formation The oldest beds of this formation belong to the Dinosaur Canyon Member, a reddish, slope-forming rock layer with thin beds of siltstone that are interbedded with mudstone and fine sandstone.
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Later, uplift exposed the Moenkopi Formation to erosion and Utah became part of a large interior basin drained by north and northwest-flowing rivers in the Upper Triassic. Shallow river deposition along with volcanic ash eventually became the mineral-rich Chinle Formation. The irregular contact zone, or unconformity, between the Chinle and the underlying Moenkopi can be seen between Rockville and Grafton in southwestern Utah. Chinle Formation Petrified wood and fossils of animals adapted to swampy environments, such as phytosaurs, lungfish, and lacustrine bivalves, have been found in this formation as well as conifer trees, cycads, ferns, and horsetails.
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The Beardmore orogeny was a mountain building event in the Neoproterozoic affecting what is now Antarctica. The event is preserved in the Trans- Antarctic Mountains, potentially in the Shackleton Range and by argillite- greywacke series in the Horlick Mountains, Queen Maud Land and the Thiel Mountains. Upright folds, asymmetric overturned or recumbent isoclinal folds first identified by Elliott in 1975 was interpreted in 1992 by Edmund Stump as indicative of compressive and convergent tectonic activity. The orogeny is expressed as an unconformity in the Transantarctic Mountains, between folded Late Proterozoic strata and overlying Early or Middle Cambrian sediments.
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The angular unconformity between the Deadwood Formation and the underlying Precambrian metamorphic rocks near Rapid City, South Dakota.At the type locality in the Black Hills of South Dakota and in many other areas, the Deadwood Formation rests unconformably on Precambrian metamorphic rocks that were exposed to a long period of erosion prior to the deposition of the formation. In western Montana, western Saskatchewan and Alberta it overlies the Middle Cambrian rocks of the Earlie Formation or the Pika Formation. In the Williston Basin it is overlain by the Winnipeg Formation in the center and by the Red River Formation near the margins.
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Pope 2004, p.47-48 The Aleman Formation has up to 70% chert, in the form of thin continuous beds of sponge spicules within calcisiltite beds or of diagenetic lenses of chert nodules within skeletal wackestone or packstone. The continuous chert beds appear to have been laid down in cool water, while the packstone was deposited in warmer water.Pope 2004, p.48-51 The Cutter Formation is mostly bioturbated tidal flat carbonate mudstone or dolomite.Pope 2004, p.51-52 The contact with the underlying El Paso Formation is an unconformity corresponding to a hiatus of about 30 million years.
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Unconformably overlying the Hangman Sandstone in the Porlock Basin is the Luccombe Breccia Formation, a presumed Permian age deposit consisting of calcareous breccia, sandstone and conglomerate which may be up to 650m thick. A further presumed unconformity separates the breccia from the mudstones of the overlying Mercia Mudstone Group which underlie the larger part of the low ground between Exmoor and North Hill. At the top of the group is a 25m thickness of mudstones with gypsum referred to as the Blue Anchor Formation. Above this are around 12m thickness of mudstones and limestone assigned to the Penarth Group.
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Newer research suggests that volcanically active midocean ridges caused a massive and sudden surge of the calcium concentration in the oceans, making it possible for marine organisms to build skeletons and hard body parts.Novel Evolutionary Theory For The Explosion Of Life Alternatively a high influx of ions could have been provided by the widespread erosion that produced Powell's Great Unconformity. An increase of calcium may also have been caused by erosion of the Transgondwanan Supermountain that existed at the time of the explosion. The roots of the mountain are preserved in present-day East Africa as an orogen.
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The lower ORS is essentially detrital material eroded from the Caledonian Mountains to the north and west and deposited in this basin south of the orogen. Its deposition continued in the early Devonian and is present as the St Maughans, Senni and Brownstones formations. During the middle Devonian, the Acadian orogeny resulted in uplift, non-deposition and erosion such that the Upper ORS sits with a slight angular unconformity on the lower ORS, middle Devonian strata being missing in this region. Mudstones dominate the lower part of the sequence but sandstones came to be more prominent towards the top.
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The top of the formation is formed by an erosional unconformity at the base of the Late Oligocene to Early Miocene Blaubok Conglomerate. The fauna from the Black Crow Limestone, especially the arsinoithere Namatherium blackcrowense and the reithroparamyid rodent Namaparamys inexpectatus indicate a Late Ypresian or Early Lutetian age for the deposits. The limestones are likely to be older than 42.5 Ma on the basis of radio-isotopic dates obtained from phonolite cobbles reworked from lavas considered to have erupted later than the limestone deposition. The carbonates could be as old as 47 ± 1 Ma, i.e.
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Sadlerochit stratigraphic column The field is an anticline structure located on the Barrow Arch, with faulting on the north side of the arch and a Lower Cretaceous unconformity on the east.Sweet, J.M., 2008, Discovery at Prudhoe Bay Oil, Blaine: Hancock House, , p. 183 Claims on petroleum seeps in the Cape Simpson area were first made in 1915 by a group consisting of T.L. Richardson, W.B. Van Valen, O. Hansen, B. Panigeo and Egowa after these last two, Eskimos, pointed out two large mounds fifty feet high and 200 feet in diameter.Sweet, J.M., 2008, Discovery at Prudhoe Bay Oil, Blaine: Hancock House, , p.
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A major unconformity in the region attests that the Ozarks were above sea level for several hundred million years from the time of the volcanism in the Precambrian until the mid-Cambrian with an erosionally produced relief of up to . The seas encroached during the late Cambrian producing the Lamotte Sandstone, thick, followed by carbonate sedimentation. Coral reefs formed around the granite and rhyolite islands in this Cambrian sea. This carbonate formation, the Bonneterre, now mostly dolomite, is exposed around the St. Francis Mountains, but extends in the subsurface throughout the Ozarks and reaches a thickness of .
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Basalt dike in orange-red Hakatai Shale along Colorado River at Hance Rapid, river mile 76.5, Grand Canyon. Isis Temple and Cheops Pyramid on a fault-block (horst), sitting on "island" of Shinumo Quartzite, unit 3 of the Unkar Group. Bottom 3 units of Unkar above Granite Gorge, and Vishnu Basement Rocks. (3.5-mi by 2.0-mi block) At Apollo Temple landform, the Cambrian Tapeats Sandstone lies above the angular Great Unconformity with strata of the 3)-Chuar Group, the striped 2)-Nankoweap Formation, the dark 1-5)-Cardenas Basalt and red 1-4)-Dox Formation below.
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The Denver Formation rests on the Arapahoe Formation, and its base is marked by the first appearance of tuffaceous sediments. It is overlain by the Dawson Arkose. In 2002 the Denver Formation was included as part of a larger unconformity-bounded unit named the D1 sequence, in order to facilitate basin- wide studies and avoid confusion arising from the lateral and vertical facies changes that occur within the Denver Basin. The base of the D1 is marked by the abrupt facies change at the top of the Laramie Formation, and its top is placed at the base of a regional paleosol series.
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In 2002 the Arapahoe Formation was included as part of a larger unconformity-bounded unit named the D1 Sequence, in order to facilitate basin-wide studies and avoid confusion arising from the lateral and vertical facies changes that occur within the Denver Basin. The base of the D1 coincides with the base of the Arapahoe Formation and is marked by the abrupt change to conglomerate at the top of the Laramie Formation. The top D1 is placed at the base of a regional paleosol series. The Denver Formation and the Dawson Arkose are also included in the D1 Sequence.
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Finally, a well-defined angular unconformity at the base of the relatively flat-lying Tonto Group separates it from the underlying faulted and folded strata of the Unkar Group and the rest of the Grand Canyon Supergroup that are typically tilted at angles of 10°–30°. (units 1-2-3 of 5 units) Shinumo Quartzite cliffs upon colorful Hakatai Shale upon horizontal thin beddings of Bass Formation (upon Vishnu Basement Rocks of Granite Gorge) (expandable high-resolution photo) The western section of the Unkar group can be highlighted in a photo of three Unkar units below Isis Temple sitting on Vishnu Basement Rocks of Granite Gorge.
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The upper part of the Nankoweap Formation consists of cliff-forming sandstones that grade irregularly upward - from red to white. This change in color has been interpreted to reflect bleaching beneath an unconformity that separates red beds of the Nankoweap Formation from dark-gray dolomites of the Galeros Formation. Because this contact lies in the middle of sheer cliffs formed by the combined sandstones of the Nankoweap Formation and the overlying dolomites of the Galeros Formation, it is not easily accessible and little is known about it. The inaccessibility of the upper contact of the Nankoweap Formation has prevented a close examination of it.
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The Volta Basin formed during the Neoproterozoic and includes the one kilometer thick sandstones and claystones of the Bambouaka Supergroup, which emplaced between 1.1 billion and 700 million years ago. In the Neoproterozoic, the Snowball Earth event led to widespread glaciation in what is now Africa. Glacial erosion created an unconformity between the Bambouaka Supergroup and the Pendjari Supergroup (also known as the Oti Supergroup), which in some cases is directly atop more ancient crystalline basement rock. The 2.5 kilometer thick, 600 to 700 million year old Pendjari Supergroup has tillite and dolomitic limestone, rich in barite and silixite at its base and siltstone and argillite in its upper layers.
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In the late 1970s and early 1980s, Delmer L. Brown, a geological engineer and gemologist, conducted the most thorough scientific exploration up to that time, concluding that the dike was at least deep and that the concentration of rough sapphires was not constant throughout the deposit. Brown found that the dike had intruded into a pre-existing fault that had been a conduit for groundwater circulation. The overlying shale, the Kibbey Formation, was deposited on an unconformity, an ancient Mississippian-age karst erosion surface, and was not intruded by the dike. This groundwater action produced collapsed zones which were intruded by the dike to form breccia zones.
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The Hassi Messaoud oil field is a Cambrian sandstone reservoir 270 m thick in a dome 3300 m deep and 1300 km2 in area of the Oued Mya structural basin.Balducchi, A., and Pommier, G., 1970, Cambrian Oil Field of Hassi Messaoud, Algeria, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, pp. 477-478. The top of the dome is marked by an unconformity at the base of the Triassic, Mesozoic sediments consisting of salt, anhydrite, shale, limestone, dolomite and marls, all overlain by Mio-Pliocene sandstone.Balducchi, A., and Pommier, G., 1970, Cambrian Oil Field of Hassi Messaoud, Algeria, AAPG Memoir 14: Geology of Giant Petroleum Fields, Tulsa: AAPG, pp.
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The Taylorsville Basin is a half-graben, with the main controlling fault forming the northwestern boundary of the basin. Subsurface data from boreholes and seismic reflection profiles, indicate that the basin was originally a series of smaller half-graben at the time of the deposition of the Doswell Group. The unconformity at the base of the overlying King George Group marks a reorganization of the rift geometry with further extension being accommodated on a single basin-bounding fault zone, giving a simple NW-thickening wedge in this upper interval. The basin was inverted during the Early Jurassic, soon after the rifting stopped, forming NE-trending folds over intrabasinal normal faults.
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The Narryer Gneiss Terrane also includes parts of the Yarlarweelor Gneiss which abuts to Nabberu Basin metamorphic sequences of the Bryah-Padbury Basins, where it is present as discontinuous slivers of metamorphic rocks, pelites, metaconglomerates and gneisses caught up within regional strike-slip oblique thrust faults. The Narryer Gneiss in this far-eastern region may form the basement to the 2.0-1.8 billion year old Proterozoic rocks, and the unconformity surface may be preserved within the thrust sheets. The Narryer Gneiss Terrane is divided into four major rock sequences (Myers 1990); the Dugel Gneiss, Meeberrie Gneiss, Manfred Complex, and unassigned polydeformed leucocratic gneisses and metasediments.
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The Jalama formation is separated by overlying sedimentary layers by an unconformity most everywhere it has been found, as the Paleocene is unrepresented in the fossil record in southern Santa Barbara County, and the stratigraphic sequence goes directly from the Cretaceous Jalama to Eocene units, including the Anita and Juncal Formations.Norris, 77-78 In his 1966 book on the geology of the central Santa Ynez Mountains, Dibblee finds the Cretaceous Jalama Formation to be in conformable contact with the Eocene Juncal in the eastern part of the Santa Ynez range, without mentioning the intervening Paleocene; in this portion of the unit there are no fossils to provide clues as to date.
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The Biozone that follows 'Zigzag' is 'Tenuiplicatus', which has no sedimentation here, unlike areas further north as seen at Ketton and Clipsham. This was a much shorter period than the earlier unconformity, however, and with further deepening of the seas across what is now north-west Northamptonshire, the Finedon Quarry area became a brackish lagoon. This was sometimes deeper, resulting in fully marine limestone, sometimes with the deposition nearing the surface again allowing the growth of plants. The resulting rocks of the Wellingborough Member have rhythmic strata of Limestone often with great quantities of oyster shells, interspersed with rootlet beds as the land emerged or submerged.
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The river passes under and adjacent to the revitalised railway now known as the West Coast Wilderness Railway. South of Queenstown on the edge of the river is the early settlement of Lynchford where a gold mine and other mining activity supported a small community in the early days of the railway. In October 2018, TasDance dancers performed in the river, as part of The Unconformity festival, to create awareness of the effects mining pollution has on river systems. The performance was entitled "Junjeiri Bullun, Gurul Gaureima" (which translates to "Shallow Water, Deep Stories") and depicted native animals moving through the water while also exploring local indigenous history.
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It is exposed in the San Rafael Reef, the Waterpocket Fold, in the Henry Mountains, with additional exposures scattered across the region from the San Rafael Reef to the Paradox Basin, and in north-central New Mexico. The thin bedding is characteristic throughout the formation, but gypsum is not found in the San Juan Basin and some conglomerate is found on the south and southwestern margins of the formation.Lucas and Anderson 1992, p.81 The formation rests conformably on the underlying Curtis Formation (Utah and western Colorado) or Todilto Formation (southwest Colorado and New Mexico) but is separated from the overlying Morrison Formation by the regional J5 unconformity.
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Supai Group with a stranded log from a pre-Glen Canyon Dam flood An unconformity of 15 to 20 million years separates the Supai Group from the previously deposited Redwall Formation. Supai Group was deposited in late Mississippian, through the Pennsylvanian and into the Early Permian time, some 320 million to 270 million years ago. Both marine and non-marine deposits of mud, silt, sand and calcareous sediments were laid down on a broad coastal plain similar to the Texas Gulf Coast of today. Around this time, the Ancestral Rocky Mountains rose in Colorado and New Mexico and streams brought eroded sediment from them to the Grand Canyon area.
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Formations of the Supai Group are from oldest to youngest (an unconformity is present at the top of each): Watahomigi (see 5a in figure 1) is a slope-forming gray limestone with some red chert bands, sandstone, and purple siltstone that is thick. Manakacha (see 5b in figure 1) is a cliff- and slope-forming pale red sandstone and red shale that averages thick in Grand Canyon. Wescogame (see 5c in figure 1) is a ledge- and slope- forming pale red sandstone and siltstone that is thick. Esplanade (see 5d in figure 1) is a ledge- and cliff-forming pale red sandstone and siltstone that is thick.
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Sloss sequences—long-running changes in sea level, described by American geologist Lawrence Sloss—played an important role in sediment deposition during the Paleozoic. The Sauk sequence formed during the Cambrian, followed by the Tippecanoe in the Ordovician, the Kaskaskia between the full immersion of the Silurian and the early Mississippian. Finally, the Absaroka sequence emplaced into the early Pennsylvanian. The Great Unconformity separates Proterozoic igneous rocks from the Lamotte Sandstone, the basal unit of the Sauk sequence which also includes the Bonneterre Dolomite, Davis Formation, Derby-Roe Run Dolomite, Potosi Dolomite and Eminence Dolomite from the Cambrian, and the Ordovician Gasconade Dolomite, Roubidoux Formation and Jefferson City Dolomite.
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The dominant plant community is a low open > forest of Eucalyptus obliqua, E. goniocalyx and E. fasciculosa, above a mid- > dense heath understorey. Common mammals in the park are Macropus fuliginosus > (western grey kangaroo) and Tachyglossus aculeatus (echidna), while over > sixty species of birds have been recorded. A walking track traverses the > length of the park... The Zoothera dauma (scaly thrush) which is a > threatened bird in South Australia due to destruction of its habitat ... can > be found in the park. Together with Warren Conservation Park to the South, > the park contains unique geological exposures of a recently discovered > unconformity between the Adelaidian sequence and a rejuvenated crystalline > basement inlier.
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Overlying the Coeymans Formation, at the top of the escarpment, the Kalkberg Formation contains brachiopods and crinoids and is interpreted as even deeper marine deposits. The New Scotland Formation contains interbedded shale and sandstone; an exposure is found in Minelot Creek, up creek of the Paint Mine parking area. The Becraft Formation overlies the New Scotland Formation and is a coarse-grained limestone with abundant crinoid debris; it is best exposed in the northern section of the park near Carrick Road, where an unconformity separates the Becraft and overlying Oriskany Sandstone. Due to its predominant limestone bedrock, the park features karst topography which includes numerous disappearing streams, caves, sinkholes, and grikes.
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Nicolaus Steno, also known as Niels Stensen, was the first to observe and propose some of the basic concepts of historical geology, called the "father of geology". One of these concepts was that fossils originally came from living organisms. The other, more famous, observations are often grouped together to form the laws of stratigraphy. James Hutton and Charles Lyell also contributed to early understanding of the Earth's history with their observations at Edinburgh in Scotland concerning angular unconformity in a rock face and it was in fact Lyell that influenced Charles Darwin greatly in his theory of evolution by speculating that the present is the key to the past.
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Carboniferous coral, Ingleton, North Yorkshire Carboniferous/Jurassic unconformity surface at Tedbury Camp. The 'classic limestone walk' is a circular 10 km route from the field centre on the north side of Malham Tarn to the village of Malham, UK via Watlowes Valley and back again via Gordale Scar. Surface depressions, typically funnel-shaped and variously known as shakeholes, sinkholes, solution hollows and dolines are very common in the Yorkshire Dales and Brecon Beacons. Typically from 1–20 m deep and 1–60 m across, they form as a result of the subsurface collapse of limestone or through the more gradual dropping of surface material into caves.
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The Silurian is a major division of the geologic timescale that started about 443.8 ± 1.5 Ma. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian ice caps were less extensive than those of the late Ordovician glaciation. The melting of ice caps and glaciers contributed to a rise in sea levels, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. Other cratons and continent fragments drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. The vast ocean of Panthalassa covered most of the northern hemisphere.
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The cliffs of Alum Bay, showing the steeply-dipping multi-coloured sands above the white Chalk, with shallower dips towards the northern end Alum Bay is the location of a classic sequence of upper Paleocene and Eocene beds of soft sands and clays, separated by an unconformity from the underlying Cretaceous Chalk Formation that forms the adjoining headland of West High Down. Due to geological folding of the Alpine orogeny, the strata in the main section of the bay are near vertical, with younger rocks with progressively lower dips to the west. The sands are coloured due to oxidised iron compounds formed under different conditions.West, I.M. and Helsby, R. 2007.
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Cambrian rocks of Araba and Naqus Formations occur throughout the region above a planar unconformity, a result of peneplaination. These red and white sandstone units have a combined thickness of about 500 m. They were deposited in a continental environment except in the northeastern part of the gulf where they become marine. The next preserved sequence is the Umm Bogma or Abu Durba Formations of lower Carboniferous age, which sit apparently conformably on the Cambrian, although the base represents a hiatus of about 150 Ma. The Umm Bogma Formation is dolomitic, while the stratigraphically equivalent Abur Durba Formation consists of black shales and mudstones.
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During the Devonian Period, this basin filled with terrestrial red beds that interfinger with marine limestone and dolomites. Before deposition was terminated by marine regression, Upper Devonian black bituminous shale accumulated in the south-east of the basin. The remaining history of the Hudson Bay basin is largely unknown as a major unconformity separates Upper Devonian strata from glacial deposits of the Pleistocene. Except for poorly known terrestrial Cretaceous fluvial sands and gravels that are preserved as the fills of a ring of sinkholes around the centre of this basin, strata representing this period of time are absent from the Hudson Bay basin and the surrounding Canadian Shield.
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This is a profile view of the evolution of the Gulf of Corinth's basin. The colored letters correspond to the cross section lines drawn on the image above. Adapted from Bell, 2008 Deposition in the Gulf of Corinth occurred in at least two phases, separated by a widespread unconformity. Deposition before 400 ka marks the first phase, likely open to the east, was filled with continental and shallow-water deposits with subsidence rates slightly exceeding sedimentation rates. Average uplift rates during the late Quaternary are estimated between 1–1.5 mm/yr on the southern margin increasing during the Holocene at 1.3–2.2 mm/yr.
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Redating of the granite in the late 1980s confirmed its age and the timing relationship between the folded Alder Group and granite. (The best age estimate is now 1664+/-17 Mya.) However, this assumed that the deformation of the pre-1700 Ma Alder Group also included the northwest-directed folding and thrusting in the Mazatzal Group. This discounted the significance of the obvious angular unconformity at the base of the Mazatzal Group. New mapping and utilization of detrital zircon geochronology during the 2010s were able to constrain the age of the youngest sediments above the Mazatzal Group involved in the classic deformation of the Mazatzal orogeny.
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In general, Upper Eagle Ford rocks deposited during the Cenomanian-Turonian boundary event (OAE2) contain much less organic matter than Lower Eagle Ford rocks, which is the reverse of organic matter trends seen in the global ocean. An unconformity occurs throughout East Texas at this level, possibly due to a lack of sediments reaching the basin during the sea-level maximum. The sea-level began to drop after the Early Turonian sea-level maximum; this is most obvious at outcrops near Langtry, Texas, where water depths became shallower than 100 ft (30 m). This limestone-rich unit is known as the Langtry Member of the Boquillas Formation.
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The geology of Westwater Canyon is very similar to nearby National Parks and Monuments such as Canyonlands National Park, Colorado National Monument, and Arches National Park. The uppermost rocks in the canyon date from the Triassic-Jurassic periods and are composed of the reddish, cliff- forming Wingate Sandstone atop the green to purple, slope-forming Chinle Formation. Within the inner gorge of Westwater, a large unconformity separates the Chinle Formation from the Precambrian basement rocks composed of metamorphic Vishnu Schist (black) and Zoroaster Granite (pink). Westwater Canyon and Ruby Canyon are the only places on the Colorado River outside of the Grand Canyon where Precambrian rocks are exposed.
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The base of the Beacon Supergroup is marked by an unconformity, and is composed of the Devonian Taylor Group, a quartzose sandstone sequence, and a Late Carboniferous to Early Jurassic Victoria Group, consisting of glacial beds, sandstone, shale, conglomerate, and coal. The Beacon Sandstone was named by Hartley T. Ferrar during Scott's Discovery Expedition (1901-1904), using the Beacon Heights survey points as reference. Glossopteris fossils dated the sandstone as Permian and linked the lithology to similar sequences in neighboring continents. Generally flat lying, the supergroup is up to 3.2 km thick, and is fairly continuous from south Victoria Land to the Beardmore Glacier along the Transantarctic Mountains.
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Koʻolau volcano appears to be unrelated to the Honolulu Volcanics, which are considered to be a separate volcanic system; sometimes the "Kokohead Volcanics" are split off from the Honolulu Volcanics. The Honolulu Volcanics constitute a late stage of volcanism which in Hawaii is known as the rejuvenated stage and the third stage of a typical Hawaiian volcano. They have a much smaller volume than the Koʻolau volcano even though their lava flows are usually thicker; the unconformity that separates the Honolulu Volcanics from the Koʻolau Volcanic Series was already recognized in the 19th century. As Hawaiian volcanoes grow, they start to sink under their weight.
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Overlying the Point Loma Formation is another Late Cretaceous deposit called the Cabrillo Formation, which crops out in various areas of Point Loma. The top of the peninsula is fairly flat, reaches an elevation of , and is capped by much younger sandstone and conglomerate deposits from the Pleistocene era, 1 million years or less in age. These flat-lying beds lie directly on top of the gently dipping Point Loma and Cabrillo formations.Marshall, Monte, The Geology and Tectonic Setting of San Diego Bay, San Diego State University The gap in the sedimentary record, called an Angular unconformity, represents about 70 million years of non-deposition and/or erosion.
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The age of these deposits is demonstrated by the presence of multiple interglacial calcretes interbedded in these glaciofluvial deposits, sequences of sediments with normal and reverse magnetostratigraphy, optically stimulated luminescence dating, and unconformity truncated clastic dikes. Based upon these criteria, Quaternary geologists estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. The older Pleistocene glaciofluvial deposits within the Hanford formation are fragmentary in nature because they have been repeatedly eroded and largely removed by subsequent Missoula floods. Because of the fragmentary nature of older glaciofluvial deposits, the exact number of older Missoula floods, which are known as Ancient Cataclysmic Floods, that occurred during the Pleistocene cannot be estimated with any confidence.
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The Carlin mine began producing gold in 1965, but at a gold price of US$35 per troy ounce, ore grades were still too low to cause a rush to northern Nevada. It was not until the gold price escalated in the 1970s that mining companies began to target similar deposits.Donald M. Hausen and Paul F. Kerr (1969) Fine gold Occurrence at Carlin, Nevada, in Ore Deposits of the United States, 1933-1968, New York: American Institute of Mining Engineers, p.908-940. The Carlin Trend, part of what is also known as the Carlin Unconformity, is wide and long running northwest–southeast, has since produced more gold than any other mining district in the United States.
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Unconformity at the base of the Potsdam Sandstone The Potsdam Sandstone lies unconformably on a surface of Precambrian metamorphic rock. It is the earliest unit in the marine-transgressive sedimentary rock sequence deposited during the early Paleozoic as sea level rose to gradually inundate the craton of the paleocontinent of Laurentia. The rock, which is formed from sediments eroded off unvegetated terrestrial landscapes and deposited in near- shore coastal environments, consists almost entirely of sand-size quartz grains held together by quartz cement. It ranges in color from gray to tan, yellow, and red, with the colors imparted by small amounts of the red iron oxide mineral hematite, Fe2O3, and the yellow iron oxide mineral goethite, FeO(OH).
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The Chuar syncline is a doubly plunging fold, which means that along the hingeline within the axis of the syncline, beds in some areas (Nankoweap Canyon) dip toward the south, and in other areas (Lava Chuar Canyon), beds dip toward the north. The Sixtymile Formation, Chuar Group, and Chuar syncline is bounded on the east by the Butte fault zone and on all other sides by the Great Unconformity and overlying Tapeats Sandstone. The hingeline of the Chuar syncline parallels the trace of the Butte fault, suggesting a genetic relationship between the syncline and the fault. In descending order, the Sixtymile Formation is underlain by the Chuar Group, Nankoweap Formation, and the Unkar Group.
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Like the former stage, the Triassic sediments were first concentrated on the west side of the basin but also appeared in the southwest as a direct result from marine transgression. The Jurassic period followed with the same marine sedimentation, but by the end of the period, sea-level began to fall leaving behind shallow marine sediments. The Cretaceous period marks a major transition as the area became unstable with the basement faults reactivating and additional deposition of 1000m of brackish non-marine/freshwater sediments along with major uplift of the basin margins. The later Cretaceous consisted of deposition almost entirely of chalk with a basin wide unconformity delineating the period between the Paleogene and Late Cretaceous.
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Sequence stratigraphy is a branch of geology that attempts to subdivide and link sedimentary deposits into unconformity bound units on a variety of scales and explain these stratigraphic units in terms of variations in sediment supply and variations in the rate of change in accommodation space (relative sea level, the combination of eustatic sea level and tectonic subsidence). The essence of the method is mapping of strata based on identification of surfaces which are assumed to represent time lines (e.g. subaerial unconformities, maximum flooding surfaces), and therefore placing stratigraphy in chronostratigraphic framework. Sequence stratigraphy is a useful alternative to a lithostratigraphic approach, which emphasizes similarity of the lithology of rock units rather than time significance.
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Hall was fascinated by James Hutton's Theory of the Earth during the late 1780s and 1790s. Hutton's theory suggested that the strata of the earth were continually being worn down or melted, thereby making the earth one giant system of materials' circulation. In the spring 1788 Hall was with Hutton and John Playfair on the boat trip east from his home at Dunglass along the Berwickshire coast to Siccar Point where they found the famous rock formation now known as Hutton's Unconformity. At this point Hall was still sceptical of the chemical viability of Hutton's theory, however, he soon reconciled these doubts and ended up publishing several papers on the chemical composition of strata.
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Ingram, 67-69 The uppermost oil- bearing stratigraphic unit is the Pliocene-age Pico Formation, which contains the Aliso, Porter, and Upper, Middle, and Lower Del Aliso zones, from top to bottom, ranging in depth from about 4,500 to 8,000 feet. Underneath the Pico is the Middle Miocene Modelo Formation, and beneath that, bounded by an unconformity, the Eocene-age Llajas Formation. Since these units are both permeable and in direct contact, they form a single productive zone, the Sesnon-Frew, the largest of the field's zones and the one used by SoCalGas for gas storage. This unit has an average depth of about 9,000 feet, and averages about 160 feet thick.
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In 2000, Jennifer A. Waggoner (South Dakota School of Mines and Technology, interning at the Lunar and Planetary Institute) and Allan H. Treiman (Lunar and Planetary Institute) used Viking imagery to geologically map Ganges Mensa, subdividing it into four units named for major rivers in India serving as tributaries to the Ganges River (Gandak, Brahmaputra, Tista, Yamuna). Mariner 9 data was used to create stereo images of the layered deposits. Waggoner submitted an abstract to the 31st Lunar and Planetary Science Conference to report on her results. In light of the use of these MOC stereo images, the researchers were unable to definitively confirm the presence of an angular unconformity proposed earlier by Goro Komatsu in 1993.
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As originally defined, the formation included all strata in the northwest Albuquerque Basin younger than the Zia Formation as then defined, except for Quaternary beds assigned to the (since-abandoned) Pantadeleon Formation.Connell 2008, p.15 Tedford and Barghoon recommended that the Cerro Conejo Member of the Zia Formation be moved to the Arroyo Ojito, since there was a significant unconformity (corresponding to a hiatus in sediment deposition of 1 to 1.6 Ma) separating the Cerro Conejo from the rest of the Zia Formation.Tedford and Barghoon 1999 In 2007, Williams and Cole recommended that the Arroyo Ojito Formation be abandoned, because the name was being used inconsistently and because the formation straddled a significant region unconformityWilliams and Cole 2007, p.
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Dark green clay with sandstone and siltstone interbeds, together up to 40 meters thick, overlies Vendian age rocks, defining the Lower Cambrian and the start of the Paleozoic. It is overlain by the Lontova Stage clays. The Vergale Stage has an angular unconformity with basement rocks in the east and contains brown oolitic ironstone, sandstone, siltstone and argillite up to 45 meters thick with the 42 meter Rausve Stage sandstone and siltstone above it. The mid-Cambrian Kybartai Stage sits above the Rausve Stage with abundant glauconite and is overlain in the west by the 67 meters of clay in the Deimena Stage or the Paneriai Stage argillite and sandstone in the east.
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Of particular interest is the somewhat broader range of approximately 53 to 48 Ma for Crescent Formation basalts on the east side of the Olympic Peninsula that overlie the Blue Mountain unit, reliably dated at 48 Ma or younger. calculated a maximal depositional age of about 48.7 Ma, while report four ages ranging from 44.7 Ma to 47.8 Ma. This structural relationship was previously understood as showing that Siletzia – or at least its northern end – was built on the continental margin. It is now argued. that the unconformity of ages can be explained by the Blue Mountain unit being thrust under Siletzia some time after 44.5 Ma, and shows that Siletiza was not necessarily emplaced along the continental margin.
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Oil in these sands is mainly found in pinch-out structures, in which oil is trapped in more permeable sub-units within impermeable sands. Underneath this unit, separated by an unconformity, is the larger Modelo Formation, consisting of several sand units: the D/M Sands (the topmost), the Hauser Sand, around below sea level, and the Ogden Sand, around below sea level. Beneath the Ogden Sand is a nodular shale unit, also grouped with the Modelo; it contains no oil. Both the Ogden and the Hauser are richly productive, while a few oil-bearing pinch-outs are found in the D/M sand, which otherwise forms an impermeable cap to the Hauser.
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Parker and Calkins in 1964 noted the association of the Klondike Mountain Formation with the gold and silver deposits of the Republic District and suggested it as a potential host to more ore deposits in the Curlew Quadrangle. The epithermal gold deposits occurring in the Sanpoil volcanics terminate directly below the unconformity where the volcanics contact the base of the Klondike Mountain Formation or sometimes penetrate into the Formation's lowest unit. Hydrothermal sinter deposits are known from the lowest portions of the Formation and are thought to represent hydrothermal eruption areas. In general the lower portions of the Formation have a large amount of hydrothermal alteration, and areas around vents are rich in pyrite and silica.
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The Mulden Group was deposited after a major unconformity created by the uplift from the Kaoko Belt and Damara Belt collisions (580-530 Ma). During this time, the Owambo Basin was drained and exposed at the surface, causing massive erosion with minimal deposition. After 530 Ma, the rebound from the uplift of the Damara orogeny had caused the Owambo Basin to sink and it again filled with water to create a shallow marine system with deposition from both continental and marine organic sources. The stages between when the Owambo Basin was a transgressive vs regressive deposition system are bounded by a black shale marker that runs through the "middle" of the Mulden Group.
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The regional, local and property geology of the Rosemont deposit consists of Precambrian sedimentary and intrusive rocks, which form the regional basement under a Palaeozoic sequence of quartzites, siltstones, and carbonate rocks. Sedimentary deposition ceased for a time during uplift and formation of a widespread unconformity in the early Mesozoic, and then resumed with the deposition of continental and shallow marine deposits.Geology and Seismotectonic Review, Vector Colorado Subsequent granitic intrusions and felsic volcanic eruptions dominated the late Mesozoic and early Cenozoic, corresponding to the Laramide Orogeny when most of the porphyry copper deposits of the region formed. Compressional tectonics during the Laramide Orogeny created both low-angle thrust faults and high-angle strike-slip faults.
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These are the youngest stages of Tuzgle volcanism and are well preserved. Radiating away from the central summit of the volcano, another lava flow unit forms the so-called Azufre synthem; these lava flows reach maximum thicknesses of and are gray to brownish-red with some evidence of hydrothermal alteration. On the northwestern and southern flanks, lava emission from one emission area down steep slopes form the San Antonio synthem (unconformity bounded unit), with lava flows up to thick. These San Antonio stage lavas have been cut by a long fault scarp trending NNE-SSW that may have been formed by a mass failure of the Tuzgle edifice, which was then rebuilt by the Azufre stage lavas.
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James I. Kirkland, 2014, "The Nature of the Jurassic/Cretaceous (J/K) Unconformity and the Early Cretaceous of Eastern Utah" In: Jim Kirkland, John Foster, ReBecca Hunt-Foster, Gregory A. Liggett, and Kelli Trujillo (eds), Mid-Mesozoic: the Age of Dinosaurs in Transition, April 30 – May 5, 2014 Fruita, Colorado & Green River, Utah p. 62-63 A second species, G. lorriemcwhinneyae, was described from the Ruby Ranch Member in 2016 based on a large bonebed, probably formed when a group died of drought or drowning. All together, more complete material exists for Gastonia than for any other basal ankylosaur. A wealth of disarticulated material from a bonebed presents problems as it can be hard to tell how many spikes a particular Gastonia actually had.
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About 18,000 years ago, during the Pleistocene Epoch of the Quaternary Period (Cenozoic Era), the level of the Pacific Ocean was considerably lower than it is now (because more water was in the polar ice- caps and continental glaciers). Deep submarine canyons were cut in the Monterey Bay area, as an extension of the Salinas River. During late Cenozoic Era, because of sustained transpression of the Pacific Plate onto the American Plate along the nearby San Andreas Fault Zone, there was continued uplift of the entire coastline of California, so that erosive action of marine waves cut these terraces in the Monterey Bay area. Those Pleistocene marine terraces are composed of clay, silt, sand and gravel with a basal unconformity of gravel on top of rock.
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The village's picturesque scenery captivated both James Guthrie and Edward Arthur Walton who shared a house there in 1883. Dunglass, just to the west of the town, was the home of the geologist Sir James Hall who, in the Spring of 1788, joined John Playfair and James Hutton in a boat trip from Dunglass Burn east along the coast looking for evidence to support Hutton's theory that rock formations were laid down in an unending cycle over immense periods of time. They found examples of Hutton's Unconformity at several places, particularly an outcrop at Siccar Point sketched by Sir James Hall. As Playfair later recalled, "The mind seemed to grow giddy by looking so far back into the abyss of time".
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The Subathu Formation was interpreted to be a preservation of the intense collision between the two plates in the western part of the foreland basin that leads to thrusting. An evidence of a silicified chert breccia strata existing just on top of the rigid precambrian basement was interpreted as a growth fault that developed as a result of compressional tectonics. The thrust slices in the sub-himalayan ranges now preserves some of the Subathu Formation. Although a debate has arise, it is inferred that some locations where the Subathu Formation is exposed are now considered to be the forebulge of the foreland basin as it is overlain by a much younger formation where a time hiatus or an unconformity has occurred.
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The Transvaal Basin is one of three basins of the Transvaal Supergroup on the Kaapvaal craton. The evolution of this 2.65–2.05 Ga Neoarchaean–Palaeoproterozoic basin is thought to have been derived largely from magmatism, palaeoclimate and eustasy, while plate tectonics played an intermittent role. The supergroup is made up of basal ‘protobasinal’ rocks, upon which followed the Black Reef Formation, Chuniespoort Group and the uppermost Pretoria Group.Encyclopædia Britannica The Transvaal Supergroup displays three unconformity-bounded sequences that surface in two geographically distinct areas – the Transvaal Basin, which circumscribes the Bushveld Igneous Complex, and the Griqualand West basin, lying between Kimberley and Sishen at the western Kaapvaal craton rim, extending into southern Botswana beneath the Kalahari Sands as the Kanye Basin.
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Gullet Quarry and unconformity The Malvern Hills are formed of some of the most ancient rocks in England, mostly igneous and metamorphic rocks from the late Precambrian, known as the Uriconian, which are around 680 million years old. The Malvern Line or Malvern Lineament is the name applied to a north–south aligned lineament which runs through the Malvern Hills and extends southwards towards Bristol and northwards past Kidderminster. It consists of a series of faults and folds which have the effect of bringing old Malvernian rocks to the surface. Being largely hard igneous rocks, they have resisted erosion better than those of the surrounding countryside and result in a striking line of hills of which the Malvern Hills are the most impressive.
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From El Sherana West, 21,316 long tons at a grade of 18.35 lb U3O8 per long ton (0.82% U3O8) were produced. At El Sherana and El Sherana West, uranium-gold mineralisation occurs in two general settings: at or near the shallow-dipping Koolpin Formation/Coronation Sandstone unconformity, where it is cut by normal and reverse faults (El Sherana pit). The host rocks are chert-banded siltstone and carbonaceous shale adjacent to sandstone (Coronation Sandstone) and altered volcanics (Pul Pul Rhyolite), in irregular zones along the contacts between cherty ferruginous shale and carbonaceous shale (El Sherana West). The ore consisted of massive pods and disseminated veinlets of pitchblende, with secondary metatorbernite, autunite, gummite and gold, with minor pyrite, galena and chalcopyrite.
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It occurs where vertically oriented Precambrian Dalradian schists are overlain by more recent cornstones in the Kinnesswood Formation of the Inverclyde Group (Lower Carboniferous), with an obvious difference in dip between the two rock layers, but he incorrectly thought that the strata were conformable at a depth below the exposed outcrop. Later in 1787 Hutton noted what is now known as the Hutton Unconformity at Inchbonny, Jedburgh, in layers of sedimentary rock visible on the banks of the Jed Water. He later wrote of how he "rejoiced at my good fortune in stumbling upon an object so interesting in the natural history of the earth, and which I had been long looking for in vain." That year he found the same sequence in Teviotdale.
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Various evidence documented along NE-SW and NW-SE sections of the India–Asia collision zone synchronize with each other, being in favour of a "one-off" collision. #Facies changes (NE-SW): stratigraphic correlations of Paleocene to early Eocene across the NE-SW orientation of the Himalayas shows that the change in depositional environment is similar in time, with no unconformity and only a few tens of meters of vertical differences. This suggests that the whole Indian continental margin collided with the Asian continental margin at approximately the same time.center #Detrital zircon age patterns (NW-SE): a transect of paleo-syncollisonal basins (59-56 Ma) on the active Asian continental margin, the point of collision and the passive Indian continental margin is considered.
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Jurassic strata is usually absent beyond the southern and northern parts of the Atlas ranges. Along the Cretaceous strata this sediments had been exposed as part of an expansive body that we probably covered the entire Atlas domain, overlapping its margins, such as the Saharan Platform, the Anti‐Atlas and the Atlas Meseta, being part of a post-rift setting. That would implicate a similar succession of the Jurassic basins in the American Atlantic margin, with a marked postrift unconformity close to the Jurassic-Cretaceous boundary. Triassic and Jurassic synrift-related deposits are present especially on the external region of the Orogenic belt of the High Altas and nearly absent in the axial region, appearing in minor amounts within confined grabens.
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Redating of the granite in the late 1980s confirmed its age and the timing relationship between the folded Alder Group and granite. (The best age estimate is now 1664+/-17 Mya.) However, this assumed that the deformation of the pre-1700 Ma Alder Group also included the northwest-directed folding and thrusting in the Mazatzal Group. This discounted the significance of the obvious angular unconformity at the base of the Mazatzal Group. New mapping and utilization of detrital zircon geochronology during the 2010s were able to constrain the age of the youngest sediments above the Mazatzal Group involved in the classic deformation of the Mazatzal orogeny. Detrital zircons from the Hopi Springs Shale in the northern Mazatzal Mountains yielded a maximum depositional age (MDA) of 1571 Mya.
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Throughout this time, the area was covered by an ancient sea and thick layers of limestone and sandstone were deposited. Permian-aged strata rich in fossil brachiopods, echinoid spines, and gastropods are the only Paleozoic rocks exposed in the Chiricahua Mountains, and reflect a shallow-marine coral reef environment. These rocks are also the oldest known rocks exposed in the Chiricahuas and were formed around 280 Ma. A 150-million- year unconformity in the Chiricahua Mountains’ geologic history occurs between the Paleozoic and earliest known Mesozoic rocks due to a period of uplift and erosion. Numerous volcanoes then formed in southeastern Arizona during the Mesozoic as oceanic crust subducted beneath the southwestern portion of the United States, resulting in continued continental growth.
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Within northwestern Arizona, southeastern Nevada, and southwestern Utah this contact is an erosional unconformity that in part consists of paleovalleys, as much as several hundred feet deep, and paleokarst that were eroded into the underlying Kaibab Limestone before the deposition of the Moenkopi Formation. These paleovalleys are often filled with conglomerates and breccias that are known as the Rock Canyon conglomerate. Within the Marble Canyon and eastern Grand Canyon regions and south into Verde Valley, upper contact of the Kaibab Limestone with the Moenkopi Formation is an erosional disconformity. This disconformity exhibits little relief and is identified by marked differences in color, topography, and rock types between tan, ledge-forming, calcareous sandstones and of the Kaibab Limestone and red, slope-forming siltstones of the Moenkopi formation.
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Perspective correlation principle allows to define the notion of conformity: sequence of layers that obey the conditions of geometrical perspective is a unit of conformity. Two neighboring units of conformity are in relation of unconformity. Here is an example that shows that the borders of undisturbed stratigraphic unit in the Middle Carboniferous (Volga-Ural oil province, Russia) initially were plains. In the central part of the area (about 100 km in diameter) were chosen three wells at distances of 10 – 15 km.. The three tops of the stratigraphic unit in the three wells are points in 3D space with coordinates x, y, z, where x and y are present the position of the well on the surface (M), and z is the thickness of the stratigraphic unit in this location.
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The Sahara Seamounts are a group of seamounts which are located in the Atlantic Ocean between southwest of the island of El Hierro, part of the Canary Islands. A number of these seamounts are placed on the sea bed at depths of almost and some summits are just below sea level. An example of this is the seamount called Echo, which is also called the Endeavour Bank, where the summit is made up of a large plateau covering an area of , at depths of between and with the slopes dropping down to into the deep. The presence of seismic lines around these seamounts show local unconformity or even sills which are quite high up among the sedimentary series and these features suggest that there was volcanic activity as late as at least the Cenozoic.
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Although some early workers included the Frenchman Formation in the overlying Ravenscrag Formation, the two are separated by the Cretaceous-Paleogene boundary and are now treated separately. The contact is abrupt but conformable, and occurs at the base of the No. 1 or Ferris coal seam of the Ravenscrag Formation. The Frenchman is separated from the underlying formations by an erosional unconformity, and depending on the depth of the erosion, the Frenchman rests on the Whitemud Formation, the Battle Formation, the Eastend Formation, or the Bearpaw Formation. It is equivalent in age to the lower part of the Scollard Formation, the lower part of the Willow Creek Formation, and the lower part of the Coalspur Formation in Alberta, and the Hell Creek Formation in Montana and North Dakota.
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In the 21st century, computer technology and software are becoming portable and powerful enough to take on some of the more mundane tasks a geologist must perform in the field, such as precisely locating oneself with a GPS unit, displaying multiple images (maps, satellite images, aerial photography, etc.), plotting strike and dip symbols, and color- coding different physical characteristics of a lithology or contact type (e.g., unconformity) between rock strata. Additionally, computers can now perform some tasks that were difficult to accomplish in the field, for example, handwriting or voice recognition and annotating photographs on the spot. Digital mapping has positive and negative effects on the mapping process; only an assessment of its impact on a geological mapping project as a whole shows whether it provides a net benefit.
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Limestone to the northeast and east of the anticline in Bottineau, Burke and Renville counties, oil and gas is trapped by anhydrite infilling or shale and siltstone cap rock in the Triassic Spearfish Formation, over an unconformity. The beach and nearshore sediments of the Tyler Formation, close to Dickinson, North Dakota also house oil, trapped in Mississippian and Pennsylvanian sediments together with a shoreline stream filled with oil-bearing sand, south of Dickinson at Rocky Ridge. In one unusual case, the oil-bearing Red Wing Structure in McKenzie County contains Mississippian strata uplifted 3000 feet higher than neighboring sediments of the same age due to a meteorite impact. Western North Dakota is notable for widespread clinker—clay, shale and sandstone baked into a material like natural brick by burning coal.
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Angular unconformity near the River Twiss above Ingleton The Craven faults The strata along the River Twiss, below Quaternary terminal moraine at Raven Ray A varied geology is found within the boundaries of the parish, ranging from rocks laid down in the Iapetus Ocean in Ordovician times, through the Carboniferous limestones of the Askrigg Block on Whernside and Ingleborough and coal measures within the Craven Basin, to the Quaternary drumlin field in Ribblehead. It is a classic field study area for students of geology. Much of the parish is dominated by Carboniferous deposits deposited on the submarine platform of the Askrigg Block, which was a relatively high area forming a shelf sea buoyed up by Devonian Wensleydale Granite. It is separated from the Craven Basin to the south and west by the Craven Fault system.
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297- 301 Visiting in 1787, the geologist James Hutton found his first example of an unconformity there and this spot is one of the most famous places in the study of geology. A group of weakly metamorphosed rocks that form the Highland Border Complex lie discontinuously along the Highland Boundary Fault. One of the most prominent exposures is along Loch Fad on Bute.Gillen (2003) pp. 89–90 Ailsa Craig, which lies some south of Arran, has been quarried for a rare type of micro-granite containing riebeckite known as "Ailsite" which is used by Kays of Scotland to make curling stones. As of 2004, 60 to 70% of all curling stones in use were made from granite from the island.Roch, John (27 October 2004) "Puffins Return to Scottish Island Famous for Curling Stones".
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Cross-cutting relations can be used to determine the relative ages of rock strata and other geological structures. Explanations: A – folded rock strata cut by a thrust fault; B – large intrusion (cutting through A); C – erosional angular unconformity (cutting off A & B) on which rock strata were deposited; D – volcanic dyke (cutting through A, B & C); E – even younger rock strata (overlying C & D); F – normal fault (cutting through A, B, C & E). Methods for relative dating were developed when geology first emerged as a natural science. Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events. The principle of uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.
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The Shinarump Conglomerate is a highly resistant coarse- grained sandstone and pebble conglomerate,Blakey and Ranney 2008, with rare lenses of mudstone, sometimes forming a caprock because of its hardness, cementation, and erosion resistance.Evensen 1958 The Shinarump is found throughout the Colorado Plateau with significant exposures as the canyon rimrock in the vicinity of Canyon De Chelly National Monument, at the north- northeast of the Defiance Plateau/Defiance Uplift. At Canyon De Chelly the Shinarump Conglomerate was laid down upon De Chelly Sandstone-(280 Ma, an erosion unconformity of 50 my), in a region at the west foothill region of the mostly north-south trending Chuska Mountains of northeast Arizona - northwest New Mexico. Just northwest of Canyon De Chelly, the Shinarump also forms a caprock in Monument Valley across the border region of northern Arizona - and southern Utah.
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The maximum flow speed approached 36 meters/second (130 km/h or 80 mph). Within the Columbia River drainage basin, detailed investigation of the Missoula floods' glaciofluvial deposits, informally known as the Hanford formation, has documented the presence of Middle and Early Pleistocene Missoula flood deposits within the Othello Channels, Columbia River Gorge, Channeled Scabland, Quincy Basin, Pasco Basin, and the Walla Walla Valley. Based on the presence of multiple interglacial calcretes interbedded with flood deposits, magnetostratigraphy, optically stimulated luminescence dating, and unconformity truncated clastic dikes, it has been estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. Because of the fragmentary nature of older glaciofluvial deposits, which have been largely removed by subsequent Missoula floods, within the Hanford formation, the exact number of older Missoula floods, which are known as ancient cataclysmic floods, that occurred during the Pleistocene cannot be estimated with any confidence.
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The onset of deformation of the Rocky Mountain fold and thrust belt was due to collisional tectonic forces that occurred on the west edge of the North American craton. This thrust and fold belt was uplifted east of the Canadian Cordillera and formed between the Middle Jurassic and Early Eocene within an easterly tapering wedge of Mesoproterozoic to early Cenozoic sedimentary rocks that were deposited in the Western Canada sedimentary basin. A profound unconformity separates the sedimentary cover from the Archean to Paleoproterozoic crystalline crust of North America. This thrust and fold belt has a thin skinned geometry as indicated by the array of thrust faults that interleave and overlap along strike and cut across strata at low to moderate angle that flatten with depth, repeat the same Cambrian to Triassic stratigraphy from thrust sheet to thrust sheet, and merge into a common basal décollement, the Rocky Mountain basal décollement.
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5)-(horizontal)-Shinarump Conglomerate, 4)-(horizontal)-Moenkopi Formation, 3)-vertical cliffs of De Chelly Sandstone, and 2)-skirts/erosion slopes of Organ Rock Formation-(horizontally bedded) The angular unconformity below is upon the 1)-low angle dipping Cedar Mesa Sandstone, commonly of southeast Utah In Monument Valley, of Arizona and south Utah, only larger landforms still contain the protective caprock of the Shinarump Conglomerate. The vertical cliffs of highly resistant De Chelly Sandstone protect the highly erodable Organ Rock Formation that forms 'erosion skirts' at the base of the vertical monuments in Monument Valley. For larger mesas, or larger connected land forms, where the more erodable overlying Moenkopi Formation, has not been lost, (with the caprock Shinarump also being undermined), larger sections of Shinarump are thus preserved. Perimeter mesas in the Monument Valley region have the caprock protecting the upper surface, plants, and alluvium from easy erosion of the landform surface.
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The discovery includes a large proportion of new taxa across much taxonomic diversity, and is characterized by pristine fossil preservation. According to Science, this was the most significant Cambrian fossil discovery in modern times. Bob also works on Burgess Shale taxa in the Wheeler formation in House Range, UT. With his work around the world on the Burgess Shale he is helping to resolve one of the great mysteries relating to the Cambrian Explosion; the mechanism for the precise preservation of these fossils. By collecting geochemical data from the many sites he has worked, he hypothesized that a combination of calcium carbonate deposits and lower levels of oxygen and sulfur in the Cambrian seas prevented the degradation of the fossils by microbes. Bob’s hypothesis with Shanan Peters relating the Cambrian Explosion to the Great Unconformity was featured on the cover of Nature in 2012.
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It is famous for being the highly-resistant mostly-horizontal unit above the 1,000 my (1 by), Great Unconformity expressed areally in the Grand Canyon of Arizona; also in other areas of Arizona and adjacent Nevada. The Tapeats Sandstone is the highly erosion-resistant unit laid upon the Vishnu Basement Rocks in the central, parts of east, and parts of west Grand Canyon, Arizona. The unit comprises the 'base horizontal unit' of the platform around Granite Gorge (Inner Gorge) on the Colorado River, and because of its hardness, creates the Tonto Platform upon which the slope-forming, Bright Angel Shale, (extensive, and distinctively soft drab-greenish), and above it low cliff-forming cliff of Muav Limestone lie. The Tapeats Sandstone and the Tonto Platform follow the Colorado River, and surrounding tributary canyons, creeks, watercourses, or washes, in a dendritic fashion, much like the branches of a tree.
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Between the middle Albian and early Cenomanian, a series of pull-apart basins developed, producing a local unconformity in the Tremp Basin. A first phase of tectonic compression commenced in the Cenomanian, lasting until the late Santonian, around 85 Ma, when Iberia started to rotate counterclockwise towards Europe, producing a series of piggyback basins in the southern Pre- Pyrenees. A more tectonically quiet posterior phase provided the Tremp Basin with a shallowing-upward sequence of marine carbonates until the moment of deposition of the Tremp Formation, in the lower section still marginally marine, but becoming more continental and lagoonal towards the top. Shortly after deposition of the Tremp Formation, the Boixols Thrust, active to the north of the Tremp Basin and represented by the Sant Corneli anticline, started a phase of tectonic inversion, placing upper Santonian rocks on top of the northern Tremp Formation.
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Sometime during the late Cretaceous period, the sea withdrew from the area that was to become the California coast in the region of Santa Barbara and Ventura, exposing the sediments that had accumulated during tens of millions of years underwater – the Espada and Jalama Formations – and they began to erode. In the early Eocene, the sea returned, resuming sediment deposition on the eroded surface, making an unconformity. The first unit deposited in the Eocene was the limestone Sierra Blanca Formation, although only north of the Santa Ynez Fault, and then the ancient sea deposited the Juncal Formation on top of the Sierra Blanca.Norris, 77-81 At this time, the crustal block on which these units were deposited was nearer to the present-day position of San Diego; it has twisted approximately 90 degrees clockwise during the last 15 million years, as part of a process of regional, extensional deformation associated with motion along the boundary of the Pacific and North American Plates.
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Cross-cutting relations can be used to determine the relative ages of rock strata and other geological structures. Explanations: A – folded rock strata cut by a thrust fault; B – large intrusion (cutting through A); C – erosional angular unconformity (cutting off A & B) on which rock strata were deposited; D – volcanic dyke (cutting through A, B & C); E – even younger rock strata (overlying C & D); F – normal fault (cutting through A, B, C & E). The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault.
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The Messinian Erosional Crisis is a phase in the Messinian evolution of the central Mediterranean basin resulting from major drawdown of the Mediterranean seawater (the "Messinian Salinity Crisis"). As outlined in numerous studies, erosional events along the margins of the Mediterranean Basin during the Messinian timespan, before and during the evaporite deposition, were common.van Dijk, J.P., Barberis, A., Cantarella, G., and Massa, E. (1998); Central Mediterranean Messinian basin evolution. Tectono-eustasy or eustato- tectonics? Annales Tectonicae, 12, n. 1-2, 7-27. Those authors showed that also predating the deposition of the first cycle of evaporites, a major erosional phase can be observed along the basin margins, corresponding to a major "relative sea level drop", associated with tectonic activity (marking the end of the so-called "Mes-1" unconformity bound depositional sequence). Following this assumption that this major event corresponds to the major Messinian drawdown, Bache et al. (2009) concluded that the Mediterranean bathymetry significantly decreased before the precipitation of central basin evaporites.
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In the early Cretaceous, Nebraska received up to 100 inches of rain a year because of high temperature conditions, at nearly three times the present rate of precipitation, carrying sediments through meandering rivers in a coastal plain and depositing them in the Western Interior Seaway. Formations such as the Graneros Shale, Carlile Shale and Greehorn Limestone that extended at greater thickness into neighboring states such as Wyoming, record a period leading up to an 88 Ma erosional unconformity in which the Western Interior Seaway expanded leading to new deposition of limestone and shale. Between 88 and 80 Ma, the Niobrara Formation formed, rich in chalk from marine plankton as well as shells and fish bones, tied to the same expansion of seas that left the earlier shales and limestone. The deepening of the seaway is marked by the youngest Cretaceous unit, the 2000 foot thick Pierre Shale, deposited from 80 to 70 Ma with a sequence of black and gray shales formed in a deep ocean environment interspersed with occasional bentonite (ashfall) deposits from ancient volcanic eruptions.
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The Narryer Gneiss Terrane has undergone many high-grade polyphase deformation events, with the most notable being at 2600 to 2700 Ma associated with granite-greenstone magmatism in the Yilgarn Craton, following an event at ~3350 Ma of amphibolite facies, resulting in widespread re-equilibration of geochronometers, preceded by a deformation loosely constrained to ~3680 Ma and another predating the Meeberrie Gneiss and postdating the Manfred Complex, between 3680 and 3730 Ma. Older structural grain is preserved in areas of low stress in subsequent deformations; the 2700 to 2600 Ma Yilgarn Craton associated deformation has overprinted most other deformations, resulting in rotation of previous structures into parallelism with NE-trending upright folds and metamorphic banding. Proximal to the Proterozoic orogens and thrust belts, the gneiss belt has become variably overprinted by later deformations. In the Bryah-Padbury Basin fold-thrust belt, Yarlarweelor Gneiss rafts exist as undeformed thrust plates of pelitic schist bounded by discrete mylonite zones, as well as deformed heavily overprinted gneiss blocks caught up within shear zones, some of which appear to preserve the unconformity surface.
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The Potomac Basin is located entirely on the North American Plate The Nanjemoy Formation belongs to two geologic groups; the Wilcox Group of the Gulf of Mexico Basin in the southernmost surface expression of the formation and the Pamunkey Group in the northern and central portions from Maryland in the north through Virginia and the Carolinas. Both geologic groups have been dated to the early Paleogene; the Paleocene and Eocene periods, or in the commonly used NALMA classification; Wasatchian, defined by the age-equivalent Wasatch Formation of Wyoming. The third-oldest unit in the Pamunkey Group is the Nanjemoy Formation that overlies the Marlboro Clay and is partly overlain by the Piney Point Formation and in many areas covered by the Miocene Calvert Formation, separated by an unconformity representing about 34 Ma. The upper surface reaches an elevation of about and is overlain in most places by the Calvert Formation (Tc). The unit is present only in the southeastern part of the map area of Washington D.C., and it reaches a maximum thickness of about .
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In 1787 James Hutton noted what is now known as Hutton's Unconformity at Inchbonny, Jedburgh, and in early 1788 he set off with John Playfair to the Berwickshire coast and found more examples of this sequence in the valleys of the Tower and Pease Burns near Cockburnspath. They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass and at Siccar Point found what Hutton called "a beautiful picture of this junction washed bare by the sea", where 345-million-year-old Old Red Sandstone overlies 425-million-year-old Silurian greywacke. In the early 19th century, the paleontology of the formation was studied intensively by Hugh Miller, Henry Thomas De la Beche, Roderick Murchison, and Adam Sedgwick—Sedgwick's interpretation was the one that placed it in the Devonian: he coined the name of that period. The term 'Old Red Sandstone' was originally used in 1821 by Scottish naturalist and mineralogist Robert Jameson to refer to the red rocks which underlay the 'Mountain Limestone' i.e.
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A number of quartzite-rhyolite successions previously associated with the Mazatal orogeny have been shown to contain both Paleoproterozoic and Mesoproterozoic formations, based on detrital zircon geochronology. The younger formations define the Picuris orogeny at 1450–1300 Mya. This has raised the question of whether the Mazatzal origeny was actually distinct from the Picuris orogeny. Silver estimated the timing of the Mazatzal orogeny as between 1715 Mya and 1650 Mya. The end of the event was based on the U-Pb age of a post-tectonic granite located near Young, Arizona and folded rocks of the Alder Group (now recognized as a pre-1700 Ma succession of rock.) In contrast, Livingston's work in the Upper Salt River Canyon utilized Rb-Sr dating techniques to estimated the timing of the Mazatzal orogeny between 1425-1380 +/-100 Mya. Further mapping in the 1970s and 1980s showed that the Mazatzal Group rested entirely an angular unconformity with sheeted dikes of the 1729 Mya Payson ophiolite and pre-1700 Mya Alder Group.
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A number of quartzite- rhyolite successions previously associated with the Mazatal orogeny have been shown to contain both Paleoproterozoic and Mesoproterozoic formations, based on detrital zircon geochronology. The younger formations define the Picuris orogeny at 1450–1300 Mya. This has raised the question of whether the Mazatzal origeny was actually distinct from the Picuris orogeny. Silver estimated the timing of the Mazatzal orogeny as between 1715 Mya and 1650 Mya. The end of the event was based on the U-Pb age of a post-tectonic granite located near Young, Arizona and folded rocks of the Alder Group (now recognized as a pre-1700 Ma succession of rock.) In contrast, Livingston's work in the Upper Salt River Canyon utilized Rb-Sr dating techniques to estimated the timing of the Mazatzal orogeny between 1425-1380 +/-100 Mya. Further mapping in the 1970s and 1980s showed that the Mazatzal Group rested entirely an angular unconformity with sheeted dikes of the 1729 Mya Payson ophiolite and pre-1700 Mya Alder Group.
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