The BGS Lexicon of Named Rock Units — Result Details

Crossdale Mudstone

Computer Code: CROM Preferred Map Code: CroM
Status Code: Full
Age range: Arnsbergian Substage (CG) — Chokierian Substage (CH)
Lithological Description: Mainly blocky grey to dark grey laminated and fossiliferous mudstone, which becomes fissile on weathering. The mudstone contains siderite mudstone lenses and nodules at some levels. There are several thin marine bands composed of dark grey, platy mudstone with scattered oblate carbonate septarian nodules. Thin beds of sandstone are present and notably common in the uppermost few metres.
Definition of Lower Boundary: Sharp basal boundary placed at the change from the sandstone-dominated Silver Hills Sandstone to the overlying mudstone-dominated Crossdale Mudstone.
Definition of Upper Boundary: Sharp upper boundary placed at the change from the mudstone-dominated Crossdale Mudstone overlain by the Accerhill Sandstone, a thickly bedded sandstone-dominated succession.
Thickness: 14 to 23m in Crossdale; estimated 165m in Dolphinholme area.
Geographical Limits: Craven Basin area, northwest England.
Parent Unit: Millstone Grit Group [See Also MIGR] (MG)
Previous Name(s): Crossdale Mudstone Formation (-2117)
Crossdale Shales (-3332)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Crossdale Beck Valley, 4km south of High Bentham, West Yorkshire. 
Reference(s):
Whittard, W F and Simpson, S, 1960. Upper Carboniferous of England, Wales and Scotland, "in" Whittard, W F and Simpson, S. Lexique Stratigraphique International, part 3a VIII, Vol.18. Centre National de la Recherche Scientifique, Paris. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
Moseley, F, 1954. The Namurian of the Lancaster Fells. Quarterly Journal of the Geological Society of London, Vol.109, 423-454. 
Brandon, A, Aitkenhead, N, Crofts, R G, Ellison, R A, Evans, D J and Riley, JN J, 1998. Geology of the country around Lancaster. Memoir of the British Geological Survey, Sheet 59 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E059 E067