The BGS Lexicon of Named Rock Units — Result Details

Alum Shale Member

Computer Code: AMSH Preferred Map Code: AS
Status Code: Full
Age range: Toarcian Age (JT) — Toarcian Age (JT)
Lithological Description: Mudstone, grey, non-bituminous, with common layers of grey calcareous concretions particularly in the lower (Hard Shale Beds) and upper (Cement Shale Beds) parts; the median part (Main Alum Shale) is softer, less silty and generally less calcareous, and weathers pale grey and yellow; fossils including ammonites, bivalves and belemnites common throughout.
Definition of Lower Boundary: Conformable: base of non-bituminous grey shaly mudstone resting upon dark grey bituminous mudstone (Mulgrave Shale Member) with a double layer of sideritic concretions (Ovatum Bed). Bed 49 on Bed 48 at Hawsker Bottoms and Whitby (Howarth, 1955). Bed xvi on Bed xv at Blea Wyke (Howarth, 1962).
Definition of Upper Boundary: Conformable: sharp change up from grey shaly mudstone with common layers of calcareous concretions into dark grey micaceous and silty mudstone with red-weathering sideritic concretions (Peak Mudstone Member): Bed 44b on Bed 44a at Blea Wyke(bed numbers of Dean, 1954), or unconformably overlain by ferruginous, pebbly sandstone, ooidal ironstone or limestone of the Dogger Formation (Middle Jurassic).
Thickness: 37m at Blea Wyke, where complete; 27m at Whitby; 40m near Osmotherley (Frost, 1998); 13.2m in Felixkirk Borehole (Ivimey-Cook and Powell, 1991), overstepped south and west by Dogger Formation; absent at Brown Moor Borehole.
Geographical Limits: Cleveland Basin: complete in Peak Trough and inferred complete in central North York Moors area, lower beds seen widely (worked for alum) but member progressively overstepped westwards and southwards by Dogger Formation (Middle Jurassic).
Parent Unit: Whitby Mudstone Formation (WHM)
Previous Name(s): Alum Shale (-14)
Alum Rock (-642)
Alum Shale Series (-643)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Continuously exposed in cliffs and foreshore between Saltwick Nab and Whitby harbour, North Yorkshire coast, up to about 26m seen. Beds 49 to 72 (part) of Howarth (1955), base on Mulgrave Shale Member seen, uppermost beds absent beneath Dogger Formation. Powell, 1984; Simms et al. 2004, pp 299-304. 
Reference Section  Fully exposed in coastal foreshore between Peak Steel and Blea Wyke Point, Ravenscar, North Yorkshire coast; overlying Mulgrave Shale Member and overlain by Peak Mudstone Member, totalling 37m in thickness, beds xvi to lviii and 39 to 44a. Bed numbers are those of Howarth (1962) and Dean (1954). Knox, 1984; Hesselbo and Jenkyns, 1995. 
Reference(s):
Ivimey-Cook, H C and Powell, J H. 1991. Late Triassic and early Jurassic biostratigraphy of the Felixkirk Borehole, North Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.48, 367-374. 
Howarth, M K, 1955. Domerian of the Yorkshire coast. Proceedings of the Yorkshire Geological Society, Vol.30, 147-175. 
Young, G and Bird, J. 1822. A geological survey of the Yorkshire coast: describing the strata and fossils occurring between the Humber and the Tees, from the German ocean to the plain of York. First edition. (Whitby: Clark.) 
Powell, J H, 1984. Lithostratigraphic nomenclature of the Lias Group in the Yorkshire Basin. Proceedings of the Yorkshire Geological Society, Vol.45, p.51-57. 
Hemingway, J E. 1974. Jurassic. 161-233 in Rayner, D H and Hemingway, J E (eds), The geology and mineral resources of Yorkshire. (Leeds: Yorkshire Geological Society.) 
Howarth, M K, 1962. The Jet Rock Series and the Alum Shales Series of the Yorkshire coast. Proceedings of the Yorkshire Geological Society, Vol.33, 381-422. 
Frost, D V. 1998. Geology of the country around Northallerton. Memoir of the British Geological Survey, Sheet 42 (England and Wales). 
Knox, R W O B. 1984. Lithostratigraphy and depositional history of the late Toarcian sequence at Ravenscar, Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 45, 99-108. 
Young, G. 1817. Mineralogy. A history of Whitby and Streoneshalh Abbey. (Whitby.) 
Smith, W. 1821. Geological map of Yorkshire. (London.) 
Dean, W T. 1954. Notes on part of the Upper Lias succession at Blea Wyke, Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 29, 161-179. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable