Crag Group

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Crag Group
Stratigraphic range: Pliocene to Pleistocene 4.4–0.78  Ma
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S
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Pg
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Red crag cliff at bawdsey cliff suffolk 30-10-2013.jpg
Red Crag Formation at Bawdsey cliff, Suffolk
Unit of Great Britain Superficial Deposits Supergroup
Sub-units Coralline Crag Formation, Red Crag Formation, Norwich Crag Formation, Wroxham Crag Formation
Underlies Dunwich Group, Albion Glacigenic Group, Britannia Catchments Group, British Coastal Deposits Group
Overlies Unconformity with Chalk Group and London Clay Formation
Thicknessup to 70 m offshore
Lithology
Primary sand
Other gravel, clay, silt, calcarenite
Location
Region Europe
CountryFlag of the United Kingdom.svg  UK
Extent East Anglia

The Crag Group is a geological group outcropping in East Anglia, UK and adjacent areas of the North Sea. Its age ranges from approximately 4.4 to 0.478 million years BP, spanning the late Pliocene and early to middle Pleistocene epochs. [1] [2] It comprises a range of marine and estuarine sands, gravels, silts and clays deposited in a relatively shallow-water, tidally-dominated marine embayment on the western margins of the North Sea basin. The sands are characteristically dark green from glauconite but weather bright orange, with haematite 'iron pans' forming. The lithology of the lower part of the Group is almost entirely flint. The highest formation in the Group, the Wroxham Crag, contains over 10% of far-travelled lithologies, notably quartzite and vein quartz from the Midlands, igneous rocks from Wales, and chert from the Upper Greensand of southeastern England. This exotic rock component was introduced by rivers such as the Bytham River and Proto-Thames. [3] [4]

The constituent formations of the Crag Group are the Coralline Crag (mid to late Pliocene); the Red Crag (late Pliocene / early Pleistocene); the Norwich Crag (early Pleistocene) and the Wroxham Crag (early to Middle Pleistocene). [5] The sedimentary record is incomplete, leading to difficulties in correlating and dating sequences [6]

The term Crag was first used in a geological sense by R.C. Taylor in 1823, a word commonly used in Suffolk to designate any shelly sand or gravel. [7]

See also

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The Bramertonian Stage is the name for an early Pleistocene biostratigraphic stage in the British Isles. It precedes the Pre-Pastonian Stage. It derives its name from Bramerton Pits in Norfolk, where the deposits can be found on the surface. The exact timing of the beginning and end of the Bramertonian Stage is currently unknown. It is only known that it is equivalent to the Tiglian C1-4b Stage of Europe and early Pre-Illinoian Stage of North America. It lies somewhere in time between Marine Oxygen Isotope stages 65 to 95 and somewhere between 1.816 and 2.427 Ma. The Bramertonian is correlated with the Antian stage identified from pollen assemblages in the Ludham borehole.

The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma and 1.806 ± 0.005 Ma. It follows the Piacenzian stage and is followed by the Calabrian stage.

The Corton Formation is a series of deposits of Middle Pleistocene age found primarily along the coasts of Suffolk and Norfolk in eastern England.

Cromer Forest Bed

The Cromer Forest Bed is a geological formation in Norfolk, England. It consists of river gravels, estuary and floodplain sediments predominantly clays and muds as well as sands along the coast of northern Norfolk. It is the type locality for the Cromerian Stage of the Pleistocene between 0.8 and 0.5 million years ago., The deposit itself range varies in age from about 2 to 0.5 million years ago. It is about 6 metres thick and is exposed in cliff section near the town of West Runton. For over a century the bed, named after the local town of Cromer, has been famous for its assemblage of fossil mammal remains, containing the diverse remains of numerous taxa, including deer, carnivorans and birds. Although most of the forest bed is now obscured by coastal defence, the Cromer Forest Bed continues to be eroded and is rich in fossils including the skeletal remains of the West Runton Mammoth which was discovered in 1990. The oldest human footprints outside Africa, the Happisburgh footprints as well as handaxes and bison bones with cut marks were also found in layers considered to belong to this deposit near the town of Happisburgh.

Bramerton Pits Site of Special Interest in Norfolk, England

Bramerton Pits is a 0.7-hectare (1.7-acre) geological Site of Special Scientific Interest north of the village of Bramerton in Norfolk on the southern banks of the River Yare. It is a Geological Conservation Review site.

Red Crag Formation

The Red Crag Formation is a geological formation in England. It outcrops in south-eastern Suffolk and north-eastern Essex. The name derives from its iron-stained reddish colour and crag which is an East Anglian word for shells. It is part of the Crag Group, a series of notably marine strata which belong to a period when Britain was connected to continental Europe by the Weald–Artois Anticline, and the area in which the Crag Group was deposited was a tidally dominated marine bay. This bay would have been subjected to enlargement and contraction brought about by transgressions and regressions driven by the 40,000-year Milankovitch cycles.

<i>Orcinus citoniensis</i> Extinct species of killer whale

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Norwich Crag Formation

The Norwich Crag Formation is a stratigraphic unit of the British Pleistocene Epoch. It is the second youngest unit of the Crag Group, a sequence of four geological formations spanning the Pliocene to Lower Pleistocene transition in East Anglia. It was deposited between approximately 2.4 and 1.8 million years ago, during the Gelasian Stage.

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The geology of Norfolk in eastern England largely consists of late Mesozoic and Cenozoic sedimentary rocks of marine origin covered by an extensive spread of unconsolidated recent deposits.

The British Coastal Deposits Group is a Quaternary lithostratigraphic group present in coastal and estuarine areas around the margins of Great Britain. They are a mix of sands, gravels, silts, clays and peat and, north of a line between the Ribble and Tyne, include glacio-eustatically raised deposits. They lie unconformably on deposits of variously the Britannia Catchments Group, Albion Glacigenic Group, Caledonia Glacigenic Group, Dunwich Group, Crag Group or earlier bedrock. Their upper boundary is the present day ground surface.

The Dunwich Group is a Pleistocene lithostratigraphic group present in England north of the upper Thames and, downstream, a line drawn east from near Marlow to Clacton-on-Sea and which encompasses river terrace deposits of the Proto-Thames and other rivers. It unconformably overlies Triassic to Pleistocene bedrock and superficial deposits. In turn it is often overlain by deposits of the Albion Glacigenic Group and sometimes by those of the Britannia Catchments Group or British Coastal Deposits Group and interfingers in places with those of the Crag Group. No deposits potentially assignable to the group have been identified north of East Anglia or the English Midlands; they are likely to have been destroyed or removed by glacial action.

The Great Britain Superficial Deposits Supergroup is a Neogene to Quaternary lithostratigraphic supergroup present across Great Britain and the Isle of Man. It includes all of the natural superficial deposits found in Great Britain and comprises the Albion Glacigenic Group, Britannia Catchments Group, British Coastal Deposits Group, Caledonia Glacigenic Group, Crag Group, Dunwich Group and Residual Deposits Group. These deposits include till, sands, gravels, silts, head, clay, peat and other materials.

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Ludham Borehole

The Ludham Borehole was a geological research borehole drilled in 1959 near Ludham, Norfolk, UK. A continuous core sample of late Pliocene and early Pleistocene sediments of the Crag Group was recovered. Analysis allowed biostratigraphic zonal schemes for fossil pollen, foraminifera, mollusca and dinoflagellates to be constructed for horizons of the Red Crag and Norwich Crag Formations, and for these formations to be thus correlated with strata of equivalent age in the North Sea basin and north-west Europe.

The Woburn Sands Formation is a geological formation in England. Part of the Lower Greensand Group, it is the only unit of the group where it occurs, and thus is sometimes simply referred to as the 'Lower Greensand' in these areas. It was deposited during the late Aptian to early Albian stages of the Early Cretaceous. The lithology consists of sandstone or loose sand with rare wisps or thin seams of clay. The formation was extensively exploited in the 19th century for the "coprolite industry", with coprolite being a local term referring to phosphate nodules of varying origins, named due to their resemblance to real coprolites. The formation contains reworked fossils of late Tithonian-Berriasian age from deposits that are no longer found locally, equivalent in age to the Sandringham Sand Formation in Norfolk and the Spilsby Sandstone of Lincolnshire, these include Dicranodonta and the ammonite Subcraspedites. Reworked dinosaur material is known from the Potton locality within the formation.

References

  1. Head, MJ (1988). Marine environmental change in the Pliocene and early Pleistocene of eastern England: the dinoflagellate evidence reviewed. In: van Kolfschoten, T and Gibbard, PL (eds): The Dawn of the Quaternary - proceedings of the SEQS-EuroMam Symposium : Kerkrade, 16-21 June 1996. Netherlands Institute of Applied Geoscience, 1998; fig.2. ISBN   9072869613.
  2. Mathers, SJ & Hamblin, RJO (2015). Late Pliocene and Pleistocene Marine Deposits. In: Lee, JR; Woods, MA; Moorlock, BSP, eds. British Regional Geology: East Anglia (5th Edition). British Geological Survey; fig.46. ISBN   978 085272 823 9
  3. The BGS Lexicon of Named Rock Units. British Geological Survey; online at http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=CRAG. Accessed October 2017
  4. Lee, JR; Woods, MA; Moorlock, BSP, eds. (2015). British Regional Geology: East Anglia (5th Edition). British Geological Survey; p.110. ISBN   978 085272 823 9.
  5. Lee, JR; Woods, MA; Moorlock, BSP, eds. (2015). British Regional Geology: East Anglia (5th Edition). British Geological Survey; p.111. ISBN   978 085272 823 9.
  6. Jones, RL & Keen, DH (1993). Pleistocene Environments of the British Isles. Chapman & Hall. ISBN   0 412 44190 X.
  7. Woodward, HB (1881): The Geology of the Country around Norwich. Memoirs of the Geological Survey of the United Kingdom; p.32