The BGS Lexicon of Named Rock Units — Result Details

Taw Valley Formation

Computer Code: TAW Preferred Map Code: notEntered
Status Code: Full
Age range: Early Pleistocene Epoch (QPE) — Holocene Epoch (QH)
Lithological Description: The formation encompasses the fluvial, lacustrine and organic deposits of the River Taw and its tributaries. It includes floodplain alluvium and the deposits of ten terraces. The floodplain alluvium comprises soft poorly sorted clays, silts and fine-grained sands, with bodies of peat, overlying sands and gravels. The terrace deposits dominantly comprise silty and sandy pebbly clays but include sands and gravels and silts. The clays are largely derived from Upper Carboniferous mudstone bedrock. Gravels are dominantly formed of rounded pebbles up to 50mm diameter of Upper Carboniferous sandstone but also include vein quartz and Lower Carboniferous limestone and chert. Boulders of Dartmoor Granite and quartz-feldspar-tourmaline rock are common in the upper reaches. All the terraces contain alluvial tin ore (cassiterite).
Definition of Lower Boundary: Unconformable upon bedrock of Late and Early Carboniferous and Permian age and upon the Dartmoor Granite.
Definition of Upper Boundary: Surface.
Thickness: Up to 22.5m recorded in the buried sub-drift valley of the 7th terrace.
Geographical Limits: The entire catchment of the River Taw and its tributaries, including the rivers Mole and Bray, from Dartmoor and Exmoor to Barnstaple, Devonshire.
Parent Unit: Cornubian Catchments Subgroup (CCAT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The valley of the River Taw from Dartmoor to Barnstaple, Devonshire. Freshney, et al., 1979. 
Reference(s):
Edmonds, E A, Wright, J E, Beer, K E, Hawkes, J R, Fenning, P J, Freshney, E C, Lovelock, P E R, McKeown, M C, Ramsbottom, W H C and Williams, M. 1968. Geology of the country around Okehampton. Memoir of the Geological Survey of Great Britain, Sheet 324 (England and Wales). 
Freshney, E C, Beer, K E and Wright, J E. 1979. Geology of the country around Chumleigh. Memoir of the Geological Survey of Great Britain, Sheet 309 (England and Wales). 
Edmonds, E A, Whittaker, A, and Williams, B J. 1985. Geology of the country around Ilfracombe and Barnstaple. Memoir of the British Geological Survey, Sheets 277 and 293 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E293 E294 E309 E319 E324