The BGS Lexicon of Named Rock Units — Result Details

Tamar Group

Computer Code: TAMA Preferred Map Code: notEntered
Status Code: Full
Age range: Emsian Age (DE) — Tournaisian Stage (CT)
Lithological Description: Mudstones with variable amounts of very subordinate thin siltstone, sandstone and limestone beds. Component mudstone formations are characterised either by grey, purple and red, or green and grey green colourations. The mudstone formations locally contain scattered units of thin- to thick-bedded limestone or sandstone. Intertonguing with the grey mudstones are thick, geographically separated formations of thick-bedded to massive shallow water bioclastic and reef limestone, locally capped by condensed nodular limestones and mudstones. Thick units of basaltic lava (spilite), massive and bedded hyaloclastite, and bedded tuff are also present in the Group.
Definition of Lower Boundary: The lower boundary is everywhere tectonic, but the Tamar Group is assumed to overline the Meadfoot Group.
Definition of Upper Boundary: The upper boundary is rarely seen due to tectonics but taken at the incoming of dark grey to black mudstones and or thin-bedded cherts of the Chudleigh Group above the grey, purple and green mudstones of the Tamar Group.
Thickness: In excess of 6700m on the north Cornish coast; possibly thicker elsewhere.
Geographical Limits: South Devon (SX 80 60) to north Cornwall (SX 00 80).
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Tamar valley, Devon and Cornwall. The area contains the full range of lithologies and intertonguing relationships of the various formations of the group. The basal contact is a thrust but the upper boundary is seen. Leveridge et al. 2002. 
Reference(s):
Leveridge B E, Holder, M T, Goode, A J J, Scrivener R C, Jones N S and Merriman, R J. 2002. Geology of the Plymouth and south-east Cornwall area. Memoir of the British Geological Survey, Sheet 348 (England and Wales). 
Waters, C N, Brown, M A E, Dean, M T and Powell, J H. In press. Lithostratigraphical framework for Carboniferous successions of Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable