British Coastal Deposits Group

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British Coastal Deposits Group
Stratigraphic range: Cromerian to Flandrian age
Type Group
Unit of Great Britain Superficial Deposits Supergroup
Thicknessup to 80m
Lithology
Primary sand
Other gravel, silt, clay. peat
Location
Country England, Scotland, Wales
Extent British Isles (not Ireland) [1]

The British Coastal Deposits Group is a Quaternary lithostratigraphic group (a sequence of rock strata or other definable geological units) 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 (with which they also interfinger), Albion Glacigenic Group, Caledonia Glacigenic Group, Dunwich Group, Crag Group or earlier bedrock. Their upper boundary is the present day ground surface. [2]

Quaternary is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene and the Holocene. The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.

Lithostratigraphy

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general a stratum will be primarily igneous or sedimentary relating to how the rock was formed.

A group in stratigraphy is a lithostratigraphic unit, a part of the geologic record or rock column that consists of defined rock strata. Groups are generally divided into individual formations. Groups may sometimes be divided into "subgroups" and are themselves sometimes grouped into "supergroups".

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The Caledonia Glacigenic Group is a Quaternary lithostratigraphic group present across the whole of Great Britain to the north and west of the furthest limit of Devensian glaciation ie throughout Scotland, Wales and northern England. It consists of a wide range of deposits deriving from the Devensian glaciation of glacial, glaciofluvial, glaciolacustrine and glaciomarine origin. It was previously known as the South Britain Glacigenic Group. Its upper boundary is the present day ground surface or an unconformable contact with the Britannia Catchments Group or the British Coastal Deposits Group.

The Britannia Catchments Group is a Quaternary lithostratigraphic group present in all parts of Great Britain and including the Isle of Man. It includes a wide range of deposits including alluvium, river terrace deposits, peat, head, cover sand and blown sand of fluvial, lacustrine, mass movement, periglacial and aeolian origin. Its lower boundary is defined as an unconformable contact with the underlying Albion Glacigenic Group, the Caledonia Glacigenic Group, the Dunwich Group, Crag Group or with older bedrock. Its upper boundary is generally the present day ground surface but it interfingers locally with the British Coastal Deposits Group.

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.

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References

  1. Terminology as per BGS reference
  2. "BGS Lexicon of Named Rock Units - Result Details". Bgs.ac.uk. Retrieved 17 January 2019.