The BGS Lexicon of Named Rock Units — Result Details

Somerset Catchments Subgroup

Computer Code: SOCA Preferred Map Code: notEntered
Status Code: Full
Age range: Anglian Stage (QA) — Holocene Epoch (QH)
Lithological Description: The Somerset Catchment Subgroup encompasses all the fluvial, lacustrine and organic deposits of the rivers whose catchments fall between the Mendip, Quantock and Blackdown hills. The deposits comprise gravels, sands, silts, clays and peats. Floodplain alluvium comprises soft silts and clays, commonly with beds of peat and a basal bed of sand and gravel. River terrace deposits are largely sands and gravels. The gravels are composed of locally-derived rocks, variously Devonian sandstones, Carbonifeous sandstones and limestones, Triassic sandstones, Jurassic limestones and Cretaceous chert and flint. Minor marine deposits may be included where they are intercalated in dominantly fluvial formations. Anglian to Holocene (MIS 12 - 1).
Definition of Lower Boundary: Formations of the Somerset Catchments Subgroup rest unconformably on bedrock varying in age from Devonian to Cretaceous.
Definition of Upper Boundary: Surface, or locally overlain by clays, silts and peats of the Somerset Levels Formation.
Thickness: About 10 m.
Geographical Limits: Somerset, constrained by the watersheds formed by the the Quantock Hills to the west, the Mendip Hills to the north and the Blackdown Hills to the south.
Parent Unit: Britannia Catchments Group (BCAT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Valley of the River Parrett and its tributaries between Martock and Westonzoyland. 
Reference(s):
McMillan, A A, Hamblin, R J O, and Merritt, J W. 2011. A lithostratigraphical framework for onshore Quaternary and Neogene (Tertiary) superficial deposits of Great Britain and the Isle of Man. British Geological Survey Research Report, RR/10/03. 343pp. 
McMillan, A A. 2005. A provisional Quaternary and Neogene lithostratigraphical framework for Great Britain. (Netherlands: Journal of Geosciences), 84-2, 87-107. 
McMillan, A A, Hamblin, R J O and Merritt, J W. 2005. An overview of the lithostratigraphical framework for the Quarternary and Neogene deposits of Great Britain (onshore). British Geological Survey Research Report RR/04/04. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable