The BGS Lexicon of Named Rock Units — Result Details

Dunwich Group

Computer Code: DUNW Preferred Map Code: notEntered
Status Code: Full
Age range: Pleistocene Epoch (QP) — Pleistocene Epoch (QP)
Lithological Description: Fluvial gravels with subsidiary sands, clays and silts. The Group comprises the interpreted fluvial terrace sequences of those rivers that were either destroyed by or, in the case of the Proto-Thames, significantly modified by, the overriding ice sheets that deposited the Albion Glacigenic Group. The pebble contents of these various gravels can be used to demonstrate the denudation history of the source areas of the sediments.
Definition of Lower Boundary: Seen as a sharp planar unconformity, resting on strata from Triassic to Pleistocene (Crag Group) in age. The unit can be distinguished from the Crag Group on the basis of the fluvial origin of the deposits of the Dunwich Group, as the Crag Group is interpreted to be marine to estuarine.
Definition of Upper Boundary: Most commonly overlain by deposits of the Albion Glacigenic Group, from which it can be distinguished by the presence of northern-British derived errratics in the Albion Glacigenic Group. It is less commonly overlain by deposits of the Britannia Catchments Group or British Coastal Deposits Group. It also interdigitates with Crag Group deposits.
Thickness: Up to c.15m
Geographical Limits: The southern limit is taken as the course of the River Thames above its point of diversion, and below that, the southern limit of the Kesgrave Catchment Subgroup; i.e. a line from SU 770 830 near Marlowe to TM 120 160 near Clacton-on-Sea. There is no northern limit but no deposits are currently identified north of East Anglia and the Midlands. Farther north all such deposits could have been destroyed by the advancing ice responsible for deposition of the Albion Glacigenic Group. Offshore the delta plain sediments of the Yarmouth Roads Formation, correlated with the Cromer Forest-bed Formation, extend over the Southern and Central North Sea basins northwards to about 55º30'N-56ºN.
Parent Unit: Great Britain Superficial Deposits Supergroup (GBG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  East Anglia Rose et al., 2001. 
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. 
Rose, J, Moorlock, B S P and Hamblin, R J O. 2000. Lithostratigraphy and palaeoenvironments of the pre-Anglian sand and gravels of East Anglia. 35-45 in Lewis, S G, Whiteman, C A and Preece (editors) The Quaternary of Norfolk and Suffolk: Field Guide. Quaternary Research Association, London. 
Rose J, Candy, I, Moorlock, B S P, Wilkins, H, Lee, J A, Hamblin, R J O, Lee, J R, Riding, J B and Morigi, A N. 2002. Early and Middle Pleistocene river, coastal and neotectonic processes, southeast Norfolk, England. Proceedings of the Geologists' Association, Vol.113, 47-67. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable