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Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.
Conglomerate is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts. A conglomerate typically contain a matrix of finer-grained sediments, such as sand, silt, or clay, which fills the interstices between the clasts. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay.
In geology, the term Torridonian is the informal name for the Torridonian Group, a series of Mesoproterozoic to Neoproterozoic arenaceous and argillaceous sedimentary rocks, which occur extensively in the Northwest Highlands of Scotland. The strata of the Torridonian Group are particularly well exposed in the district of upper Loch Torridon, a circumstance which suggested the name Torridon Sandstone, first applied to these rocks by James Nicol. Stratigraphically, they lie unconformably on gneisses of the Lewisian complex and their outcrop extent is restricted to the Hebridean Terrane.
The Roxbury Conglomerate, also informally known as Roxbury puddingstone, is a name for a rock formation that forms the bedrock underlying most of Roxbury, Massachusetts, now part of the city of Boston. The bedrock formation extends well beyond the limits of Roxbury, underlying part or all of Quincy, Canton, Milton, Dorchester, Dedham, Jamaica Plain, Brighton, Brookline, Newton, Needham, and Dover. It is named for exposures in Roxbury, Boston area.
The Ecca Group is the second of the main subdivisions of the Karoo Supergroup of geological strata in southern Africa. It mainly follows conformably after the Dwyka Group in some sections, but in some localities overlying unconformably over much older basement rocks. It underlies the Beaufort Group in all known outcrops and exposures. Based on stratigraphic position, lithostratigraphic correlation, palynological analyses, and other means of geological dating, the Ecca Group ranges between Early to earliest Middle Permian in age.
The Clarens Formation is a geological formation found in several localities in Lesotho and in the Free State, KwaZulu-Natal, and Eastern Cape provinces in South Africa. It is the uppermost of the three formations found in the Stormberg Group of the greater Karoo Supergroup rocks and represents the final phase of preserved sedimentation of the Karoo Basin.
The Tumblagooda Sandstone is a geological formation deposited during the Silurian or Ordovician periods, between four and five hundred million years ago, and is now exposed on the west coast of Australia in river and coastal gorges near the tourist town of Kalbarri, Kalbarri National Park and the Murchison River gorge, straddling the boundary of the Carnarvon and Perth basins. Visible trackways are interpreted by some to be the earliest evidence of fully terrestrial animals.
The Triassic Lockatong Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It is named after the Lockatong Creek in Hunterdon County, New Jersey.
The Belt Supergroup is an assemblage of primarily fine-grained sedimentary rocks and mafic intrusive rocks of late Precambrian (Mesoproterozoic) age. It is more than 15 kilometres (10 mi) thick, covers an area of some 200,000 km2, and is considered to be one of the world's best-exposed and most accessible sequences of Mesoproterozoic rocks. It was named after the Big Belt Mountains in west-central Montana. It is present in western Montana and northern Idaho, with minor occurrences in northeastern Washington and western Wyoming. It extends into Canada where the equivalent rocks, which are called the Purcell Supergroup, are exposed in southeastern British Columbia and southwestern Alberta. The rocks of the Belt Supergroup contain economically significant deposits of lead, zinc, silver, copper, gold, and other metals in a number of areas, and some of the Belt rocks contain fossil stromatolites.
The Stormberg Group is one of the four geological groups that comprises the Karoo Supergroup in South Africa. It is the uppermost geological group representing the final phase of preserved sedimentation of the Karoo Basin. The Stormberg Group rocks are considered to range between Lower Triassic (Olenekian) to Lower Jurassic (Pliensbachian) in age. These estimates are based on means of geological dating including stratigraphic position, lithostratigraphic and biostratigraphic correlations, and palynological analyses.
Uriconian rocks are volcanic rocks found in parts of Shropshire, United Kingdom. The name relates to Uriconio, the Latin name for an Iron Age hillfort on the summit of the Wrekin, a hill formed of Uriconian rock.
The Longmyndian Supergroup is a 6,000-metre-thick (20,000 ft) sequence of Late Precambrian rocks that outcrop between the Pontesford–Linley Fault System and the Church Stretton Fault System in the Welsh Borderland Fault System. The supergroup consists of two major geological groups, the Stretton Group and the overlying Wentnor Group. The rocks are a generally regressive sequence from basinal facies to clastic sedimentation. The rocks are thought to be derived from Uriconian mountains that were formed during the southward subduction of an oceanic plate beneath a continental block. The rocks have since been folded due to fault movements and plunge gently to the south.
The Wrekin Terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes in the region are the Charnwood Terrane, Fenland Terrane, Cymru Terrane and the Monian Composite Terrane. The Wrekin Terrane is bounded to the west by the Welsh Borderland Fault System and to the east by the Malvern Lineament. The geological terrane to the west is the Cymru Terrane and to the east is Charnwood Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.
The Cymru Terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes are the Charnwood Terrane, Fenland Terrane, Wrekin Terrane and the Monian Composite Terrane. In this article the definition of terrane is that implying rocks associated with the composition of the Precambrian basement. The Cymru Terrane is bounded to the northwest by the Menai Strait Fault System and to the southeast by the Pontesford Lineament. The geological terrane to the west is the Monian Composite Terrane and to the east is Wrekin Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.
The Stretton Group is a group of rocks associated with the Longmyndian Supergroup of Ediacaran age, in Shropshire, England. The rocks are located within the tract between two elements of the Welsh Borderland Fault System, the Church Stretton Fault and the Pontesford-Linley Lineament.
The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion prior to deposition of the Tapeats Sandstone.
The Guaratiba Group is a geological group of the Santos Basin offshore of the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. The group forms the pre-salt layer in the petroleum-rich basin and hosts the biggest oil fields of Brazil, as Tupi, Júpiter and many more. The group contains, depending on the definition, three to four formations and dates to the Early Cretaceous period; Hauterivian to Early Aptian epochs. The total thickness of the group, representing the first phase of sedimentation after the break-up of Gondwana in the Santos Basin, is estimated at 4,200 metres (13,800 ft).
The Omingonde Formation is an Early to Middle Triassic geologic formation, part of the Karoo Supergroup, in the western Otjozondjupa Region and northeastern Erongo Region of north-central Namibia. The formation has a maximum thickness of about 600 metres (2,000 ft) and comprises sandstones, shales, siltstones and conglomerates, was deposited in a fluvial environment, alternating between a meandering and braided river setting.
The Teekloof Formation is a geological formation that forms part of the Beaufort Group, one of the five geological groups that comprises the Karoo Supergroup in South Africa. The Teekloof Formation is the uppermost formation of Adelaide Subgroup deposits West of 24ºE and contains Middle to Late Permian-aged deposits and four biozones of the Beaufort Group. It overlies the Abrahamskraal Formation. The Teekloof Formation does not underlie other units other than the younger Karoo dolerites and sills that relate to the emplacement of the Early Jurassic Drakensberg Group to the east. Outcrops and exposures of the Teekloof Formation range from Sutherland through the mountain escarpments between Fraserburg and Beaufort West. The northernmost localities of the Teekloof Formation are found by Loxton, Victoria West and Richmond.
The Vasquez Formation (Tvz) is a geologic formation cropping out at the eponymous Vasquez Rocks in southern California. The formation dates to the Late Oligocene to Early Miocene.
References
- 1 2 3 4 P. J. Brenchley, P. F. Rawson The Geology of England and Wales, 2006, 2nd ed.
- ↑ J. N. Carney, J. M. Horak, et al., Precambrian Rocks of England and Wales, Joint Nature Conservation Committee. Geological Conservation Review Series 20
- ↑ Pharaoh, T. C., Gibbons, W., Precambrian Rocks in England and Wales south of the Menai Strait Fault System, 1987 A Revised Correlation of the Precambrian Rocks in the British Isles
- 1 2 3 W. Compston, A. E. Wright, P. Toghill, "Dating the Late Precambrian volcanicity of England and Wales". 2002, Journal of the Geological Society of London. 159 323-339.
- 1 2 3 4 J. C. Pauley, “A revision of the stratigraphy of the Longmyndian Supergroup, Welsh Borderland, and its relationship to the Uriconian Volcanic Complex”, 1991, Geological Journal. 26 167-183