The BGS Lexicon of Named Rock Units — Result Details

Craig Rofft Sandstone Member

Computer Code: CRRS Preferred Map Code: notEntered
Status Code: Full
Age range: Brigantian Substage (CX) — Brigantian Substage (CX)
Lithological Description: Red and purple, fine- to medium-grained, sandy limestone (grainstone) and calcareous sandstone with scattered quartz pebbles and lenses of coarse shell material. Lower part is bioturbated and mottled; upper 2m are cross-stratified. The sandstone forms the upper part of a Brigantian shoaling-upwards cycle and formed in a shallow water, upper shoreface setting. The Craig Rofft Sandstone is currently shown on Sheet 94 within the Great Orme Limestone, a redundant Asbian formation now superceded by the Loggerheads Limestone Formation. However, unpublished foraminiferal dating by BGS has shown that limestones underlying the limestone member are Brigantian in age. These limestones therefore equate with the Cefn Mawr Limestone Formation and their lithology (dark grey packstones) confirms that they should be included in that formation, as must the Craig Rofft Sandstone.
Definition of Lower Boundary: Base not exposed, but should be taken at entry of sandy limestones and calcareous sandstones above underlying sand-free limestones of the Cefn Mawr Limestone Formation.
Definition of Upper Boundary: Undulating upper surface of calcareous sandstone beneath a thin, impersistent, calcretised porellanous limestone bed exposed in Craig Rofft Quarry.
Thickness: 4 to 5m
Geographical Limits: Great Orme at Llandudno (SH 76 83), North Wales.
Parent Unit: Cefn Mawr Limestone Formation (CFML)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Partial Type Section  Disused sandstone quarry on Craig Rofft, 180m east of tram shed, on the Great Orme which exposes the upper 3.4m of the member. Smyth, 1925. 
Warren, P T, Price, D, Nutt, M J C and Smith, E G. 1984. Geology of the country around Rhyl and Denbigh. Memoir for 1:50 000 geological sheets 95 and 107 and parts of sheets 94 and 106. 
Smyth, L B, 1925. A contribution to the geology of Great Ormes Head. Scientific Proceedings of the Royal Dublin Society, Vol.18, 141-164. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: