The BGS Lexicon of Named Rock Units — Result Details

Trawden Limestone Group

Computer Code: TRLI Preferred Map Code: TRLI
Status Code: Pending Upgrade
Age range: Chadian Substage (CI) — Brigantian Substage (CX)
Lithological Description: A pale to dark grey, typically darker towards the base, micritic to crystalline limestone, with subordinate partings and thin beds of calcareous mudstone, locally abundant chert, crinoid and brachiopod debris. A pale grey, fine- to medium-grained dolostone is locally present, near the base of the group.
Definition of Lower Boundary: A conformable base of argillaceous dolostone (Holme Chapel Borehole) or dark grey to black blocky claystone ,grading upward into medium to dark grey micritic limestone of the Trawden Limestone Group, above pale grey medium-grained sandstone with siliceous and dolomitic cement ,interbedded with medium to dark grey fine-grained sandstone, with an argillaceous and dolomitic matrix of the Roddlesworth Formation (Roddlesworth Borehole). Evident as a sharp change from highly serrated and high gamma responses below, and generally lower and more subdued gamma ray responses above the boundary.
Definition of Upper Boundary: A conformable base of overlying dark brown to black, calcareous and carbonaceous claystone to siltstone, of the Bowland Shale Formation above pale grey limestone of the Trawden Limestone Group.
Thickness: Thickest development of 1055 m in the type locality, and 422 m in the Holme Chapel Borehole.
Geographical Limits: Not proved at outcrop, but proved in the subsurface over the Central Lancashire High, a SW-NE structure extending from Chorley [SD 60 20] to Bradford [SE 10 30], bounded to the NW by the Pendle Fault and the Bowland Basin, and to the SE by the Rossendale Basin.
Parent Unit: Carboniferous Limestone Supergroup (CL)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  Roddlesworth No.1 Borehole (SD62SE/274) from about 1277 m to 2331 m, displaying the entire thickness of the group. 
Reference Section  Holme Chapel No.1 Borehole (SD82NE/68), from 1940 m to 1517.8 m, displaying the entire thickness of the group. 
Waters, et al., in prep. BGS lithostratigraphical framework for Carboniferous successions of southern Great Britain [Onshore] 
Evans, D J, and Kirby, G A. 1999. The architecture of concealed Dinantian carbonate sequences over the Central Lancashire and Holme highs, northern England. Proceedings of the Yorkshire Geological Society, Vol. 52, 297-312. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E075 E076