The BGS Lexicon of Named Rock Units — Result Details

Tamar Valley Formation

Computer Code: TAVA 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 Tamar and its tributaries. It includes floodplain alluvium and the deposits of eight 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 and Devonian 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 and Devonian limestone and chert. Tin ore (cassiterite) occurs in the deposits near the Bodmin Granite.
Definition of Lower Boundary: Unconformable on bedrock of Carboniferous and Devonian age, and on intrusive igneous rocks.
Definition of Upper Boundary: At the land surface.
Thickness: Up to c.10m
Geographical Limits: The entire catchment of the River Tamar and its tributaries, including the rivers Ottery and Thrushel, from near Holsworthy to the sea near Plymouth, Devonshire.
Parent Unit: Cornubian Catchments Subgroup (CCAT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Area  The valley of the River Tamar from near Holsworthy to near Plymouth, Devonshire. McKeown et al 1973. 
McKeown, M C, Edmonds, E A, Williams, M, Freshney, E C and Masson Smith, D J. 1973. Geology of the country around Boscastle and Holsworthy. Memoir of the British Geological Survey, sheets 322 and 323 (England and Wales). 
Reid, C, Barrow, G, Sherlock, R L, MacAlister, D A and Dewey, H, 1911. The geology of the country around Tavistock and Launceston. Memoir of the Geological Survey of Great Britain, Sheet 337 (England and Wales). 
Freshney, E C, Edmonds, E A, Taylor, R T and Williams, B J. 1979. Geology of the country around Bude and Bradworthy. Memoir of the Geological Survey of Great Britain, sheets 307 and 308 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E307 E322 E323 E337