The BGS Lexicon of Named Rock Units — Result Details

Shrewsbury Glacigenic Formation

Computer Code: SHREW Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Stratified sand and gravel with interbeds of laminated clay, silt and diamict (till), all characteristically containing Lower Palaeozoic clasts derived from the Welsh Massif.
Definition of Lower Boundary: Unconformable on elements of the Stockport Glacigenic Formation (after Bowen, 1999) at the stratotype locality, and locally on the Merion Till Member (Plynlimon Glacigenic Formation)in the Shrewsbury area (Thomas, 1989). At some locations farther north, it interdigitates with glacigenic deposits of the Irish Sea Coast Glacigenic Subgroup derived from the Irish Sea Basin in a complex manner (Worsley, 2005; Cannell, 1982). Locally, it overlies bedrock unconformably.
Definition of Upper Boundary: Irregularly overlain at the stratotype locality by Late Glacial solifluction deposits and thence Windermere interstadial peat (Worsley, 1991) of the Britannia Catchments Group. Elsewhere provides the present ground surface or is overlain unconformably by fluvial deposits of the Severn and Avon Catchments Subgroup.
Thickness: Up to c.6m at the stratotype locality.
Geographical Limits: Shropshire lowlands to the west of Shrewsbury and Dorrington, in a narrow band (5 to 10km wide) as far as Wrexham (Worsley, 1991).
Parent Unit: Wales Glacigenic Subgroup (WALES)
Previous Name(s): Boulder Clay (BOC)
Fluvio-Glacial Flood Gravels (-3029)
Alternative Name(s): Shrewsbury Formation
Stratotypes:
Type Section  Mousecroft Lane Quarry (abandoned), southwest suburbs of Shewsbury. A complex of ice-marginal glacigenic sediments deposited by Welsh ice (Severn Glacier) during its advance and retreat in a 5-10 km wide zone of interaction with the Irish Sea Ice sheet extending from Wrexham to Shrewsbury (Worsley, 2005). The sequence coarsens upwards from laminated muds into sand and gravel, reflecting sandur progradation, and is overlain by till. Its contact with the underlying sequence of Irish Sea Ice derived till and outwash (Stockport Glacigenic Formation, after Bowen, 1999) shows large scale, low amplitude wave-line deformation attributed to the meltout of buried ice within the latter. 
Reference(s):
Pocock R W, Whitehead T H, Wedd C B and Robertson T. 1938. Shrewsbury District including the Hanwood Coalfield. Memoir of the Geological Survey of Great Britain, England and Wales. (London: H.M.S.O.). 
Bowen, D Q, 1999. Wales. Chapter 7 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No.23. 
Worsley, P. 2005. The Cheshire-Shropshire Plain. Chapter 5 in Lewis, C A and Richards, A E (editors), The glaciations of Wales and adjacent areas. (Logaston Press.) 
Worsley, P. 1991. Glacial deposits of the lowlands between the Mersey and Severn rivers. 203-211 in Ehlers, J, Gibbard, P L and Rose, J (editors), Glacial deposits in Great Britain and Ireland. 
Cannell, B. 1982. The sand and gravel resources of the country around Shrewsbury, Shropshire: Description of 1:25 000 sheets SJ41 and SJ51. Mineral Assessment Report, Institute of Geological Sciences, 90, 149pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E152