The BGS Lexicon of Named Rock Units — Result Details

Gronant Group [Obsolete Name And Code: See CLWYD And CRAV]

Computer Code: GRN Preferred Map Code: notEntered
Status Code: Index Level
Age range: Brigantian Substage (CX) — Brigantian Substage (CX)
Lithological Description: Limestones and dolomites with cherts overlying dark limestones with mudstone partings.
Definition of Lower Boundary: Drawn at the base of the Teila Formation at Prestatyn where dark fine-grained argillaceous mudstones rest unconformably upon reef limestone.
Definition of Upper Boundary: Drawn at the conformable upward passage of the Pentre Cherts where cherts with thin calcite and dolomitic beds are conformably overlain by fossiliferous mudstones.
Thickness: 145 metres - 180 metres.
Geographical Limits: Areas around Prestatyn and Great Orme.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Prestatyn and Great Orme. 
Reference(s):
George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottam, W H C, Sevastopulo, G D and Wilson, R B. 1976. A correlation of the Dinantian rocks of the British Isles. Special Report of the Geological Society of London, No 7. 
George, T N, 1974. Lower Carboniferous rocks in Wales, pages 85-115. in the Upper Palaeozoic and post-Palaeozoic rocks of Wales. "In" Owen, T R, (Editor). Cardiff University of Wales Press. 
Somerville, I D, 1979. Minor sedimentary cyclicity in Late Asbian (Upper D1) Limestones in the Llangollen district of North Wales. Proceedings of the Yorkshire Geological Society, Vol.42, p.317-341. 
Definition not published. 
Ramsbottom, W H C, 1984. The Lower Carboniferous (Dinantian). p.107-127. "In" WARREN, P T. and others. Geology of the country around Rhyl and Denbigh. Memoirs of the British Geological Survey, Sheets 95 and 107. (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E094