The BGS Lexicon of Named Rock Units — Result Details

Nothe Grit Member

Computer Code: NGT Preferred Map Code: NGt
Status Code: Full
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Sandstone, grey to yellow to brown, fine-grained, sub-rounded grains, fairly well-sorted, argillaceous, in thick beds, with pervasive bioturbation (including Thalassinoides and Rhizocorallium). A bed with abundant sponge spicules forms a prominent calcareous cemented unit near the middle of the member. Large calcareous concretions (up to 1m) are common in many beds. Oysters, ammonites and serpulids occur in the sandstone. The uppermost part of the member (sensu BGS) is a 1.5m-thick bed of shelly, calcareous, medium-grained sandstone (Preston Grit Member of Wright, 1986), which is separated from the underlying succession by a sharp erosion surface, interpreted as a minor unconformity by Coe (1995).
Definition of Lower Boundary: The sharp, probably non-sequential, boundary with the underlying Oxford Clay Formation. This is marked by the upward change from the mudstone of the Oxford Clay to the sandstone of the Nothe Grit Member.
Definition of Upper Boundary: Gradational boundary, over several centimetres, from calcareous sandstone of the uppermost Nothe Grit (= topmost Preston Grit Member of Wright, 1986) to sandy mudstone of the overlying Nothe Clay Member.
Thickness: 10.5m (including the Preston Grit Member of Wright, 1986.
Geographical Limits: South Dorset.
Parent Unit: Redcliff Formation (RECF)
Previous Name(s): LOWER CALCEREOUS GRIT
NOTHE FORMATION
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Wave-cut platform exposed at low tide on south side of Nothe Point, Weymouth. Uppermost 7m of Member exposed. 
Reference Section  Redcliffe Point, Osmington, Dorset. Basal beds of Nothe Grit exposed at Ham Cliff, 250m to the northeast and remainder visible in low cliffs 300m to northwest of Point. 
Reference(s):
Wright, J K. 1986. A new look at the stratigraphy, sedimentology and ammonite fauna of the Corallian Group (Oxfordian) of south Dorset. Proceedings of the Geologists' Association, Vol.97, 1-21. 
Arkell, W J, 1947. The geology of the country around Weymouth, Swanage, Corfe and Lulworth. Memoir of the Geological Survey of Great Britain. 
Blake, J F and Huddleston, W H 1877. On the Corallian rocks of England. Quarterly Journal of the Geological Society of London, Vol.33, 260-405. 
Coe, A L. 1995. A comparison of the Oxfordian successions of Dorset, Oxfordshire and Yorkshire. 151-172 in Taylor, P D (Ed.) Field Geology of the British Jurassic. [Bath: The Geological Society.] 
Newall, A J. 2000. Fault activity and sedimentation in a marine rift basin (Upper Jurassic, Wessex basin, UK). Journal of the Geological Society, London, Vol.157, 83-92. 
Wright, J K and Cox, B M, 2001. British Upper Jurassic Stratigraphy. Geological Conservation Review Series No.21. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E341 E342 E343