The BGS Lexicon of Named Rock Units — Result Details

Severn and Avon Catchments Subgroup

Computer Code: SACA Preferred Map Code: notEntered
Status Code: Full
Age range: Mid Pleistocene Epoch (QPM) — Holocene Epoch (QH)
Lithological Description: The Severn and Avon Catchments Subgroup encompasses all the fluvial, lacustrine and organic deposits of the rivers that occupy the catchment areas of the River Severn, the Warwickshire Avon, the Bristol Avon, those rivers which flow from Wales into the Bristol Channel as far as Port Talbot, and all their tributaries. 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 sand and gravel. The gravels include a wide range of Palaeozoic and Mesozoic rocks, and much glacial material. Peat is a minor component, and minor marine deposits are included where they are intercalated in dominantly fluvial formations.
Definition of Lower Boundary: Formations of the Severn and Avon Catchments Subgroup rest unconformably on glacial and periglacial deposits and on a wide range of Palaeozoic and Mesozoic bedrock.
Definition of Upper Boundary: Surface.
Thickness: To c.10m
Geographical Limits: The entire area covered by the catchments of the River Severn, the Warwickshire Avon, the Bristol Avon, those rivers which flow from Wales into the Bristol Channel as far west as Port Talbot, and all of their tributaries.
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  The valleys of River Severn, Warwickshire Avon, Bristol Avon, and those rivers that flow from Wales into the Bristol Channel as far west as Port Talbot, and all of their tributaries. McMillan et al., 2005. 
Reference(s):
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