The BGS Lexicon of Named Rock Units — Result Details

Hodder Mudstone Formation

Computer Code: HOM Preferred Map Code: HoM
Status Code: Full
Age range: Chadian Substage (CI) — Holkerian Substage (CQ)
Lithological Description: Predominantly grey to dark grey mudstone, with subordinate and variable detrital limestone, siltstone and sandstone. Mudmound reef (Waulsortian) limestones, limestone boulder conglomerates and breccias locally, near the base. Soft sediment deformation, slumps, debris flows and gravity slides are widespread.
Definition of Lower Boundary: The contact with the underlying Clitheroe Limestone Formation is unconformable and shows considerable regional overstep. Many sections show a sharp lithological change from pale grey wackestone limestone of the Clitheroe Limestone Formation to grey mudstone or, locally, limestone conglomerate.
Definition of Upper Boundary: Taken where grey mudstone with subordinate limestone, siltstone and sandstone, passes up into the pale olive and blue-grey to cream-coloured porcellanous mottled wackestone, of the Hodderense Limestone Formation.
Thickness: To 900m
Geographical Limits: Craven Basin, Lancaster [SD 46] to Skipton [SD 95].
Parent Unit: Craven Group (CRAV)
Previous Name(s): Nappa Shale And Limestone Member [Obsolete Name And Code: Part Of HOM] (NSL)
Worston Shales [Obsolete Code: Use WSG] (WRSH)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The lowermost exposed beds are on the north bank of the River Hodder 1.8km eastnortheast of Doeford Bridge. The top of the formation is seen 4.8km to the southeast on the southwest bank of the river, 0.5km southeast of Higher Hodder Bridge. 
Reference(s):
Riley N J. 1990. Stratigraphy of the Worston Shale Group (Dinantian) Craven Basin, north-west England. Proceedings of the Yorkshire Geological Society, Vol. 48, 163-187. 
Gawthorpe, R L and Clemmey, H, 1985. Geometry of submarine slides in the Bowland Basin (Dinantian) and their relation to debris flows. Journal of the Geological Society of London, Vol.142, 555-565. 
Miller, J and Grayson, R F. 1972. Origin and structure of the Lower Visean "reef" limestones near Clitheroe, Lancashire. Proceedings of the Yorkshire Geological Society, Vol. 38, 607-638. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E059 E067 E068 E069