The BGS Lexicon of Named Rock Units — Result Details

Weymouth Member

Computer Code: WEY Preferred Map Code: Wey
Status Code: Full
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Predominantly pale grey, blocky, smooth, calcareous mudstones, generally only slightly silty. Thin, dark grey, carbonaceous beds with striking interburrowing at intervals. Thin calcareous siltstones may occur. Poorly fossiliferous. Large Gryphaea are characteristic; ammonite fauna usually pyritised, locally associated with sideritic nodules.
Definition of Lower Boundary: Top of Lamberti Limestone (where present) or an equivalent shell bed or siltstone. This horizon can be clearly picked on geophysical logs. Change in Gryphaea faunas (G. lituola below to G. dilatata, above) and ammonite faunas (Kosmoceras, below; Cardioceras, above) useful supportive indicators.
Definition of Upper Boundary: At upward change to more silty lithologies of West Walton Formation or its more sandy correlatives (eg Nothe Grit); commonly transitional and necessarily arbitrary. Most easily positioned where minor disconformity present. Upward change in faunal preservation from three-dimensional pyritised forms, below, to crushed clay casts, above, where Gryphaea specimens are increasingly large.
Thickness: 0 - 70m
Geographical Limits: Dorset to North Yorkshire.
Parent Unit: Oxford Clay Formation (OXC)
Previous Name(s): Upper Oxford Clay Member [Obsolete Name And Code: See WEY] (UOXC)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Coastal cliff section, Furzy (or Jordan) Cliff, Weymouth, Dorset. 
Partial Type Section  Coastal cliff section, Ham Cliff, Weymouth, Dorset. 
Reference(s):
Woodward, H B. 1895. the Jurassic Rocks of Britain. The Middle and Upper Oolitic rocks of England (Yorkshire excepted). Vol.5. Memoir or the Geological Survey of the United Kingdom. 
Berridge, N G, Pattison, J, Samuel, M D A, Brandon, A, Howard, A S, Pharaoh, T C and Riley, N J. 1999. Geology of the Grantham district. Memoir of the British Geological Survey, sheet 127 (England and Wales). 
Wright, J K, 1986. The Upper Oxford Clay at Furzy Cliff, Dorset: stratigraphy, palaeoenvironment and ammonite fauna. Proceedings of the Geologists' Association, Vol.97, p.221-228. 
Cox, B M, Hudson, J D and Martill, D M, 1992. Lithostratigraphic nomenclature of the Oxford Clay (Jurassic). Proceedings of the Geologists' Association, Vol.103, p.343-345. 
Arkell, W J. 1947. Geology of the country around Weymouth, Swanage, Corfe and Lulworth. Memoir of the British Geological Survey. Sheets 341, 342, 343 and small portions of sheets 327, 328 and 329 (England and Wales). 
Martell, D M and Hudson, J D, (Editors), 1991. Fossils of the Oxford Clay. Palaeontological Association Field Guide to Fossils No.4. 
Buckman, S S. 1923. Type ammonites Volume 4. (London.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E127 E237 E159 E219