The BGS Lexicon of Named Rock Units — Result Details

Ridgeway Member

Computer Code: RID Preferred Map Code: Rid
Status Code: Full
Age range: Tithonian Age (JI) — Berriasian Age (KR)
Lithological Description: In west Dorset, comprises dark greyish brown, carbonaceous muds and pale marls and micrites, commonly containing thin detrital quartz laminations that form isolated ripples. The mudstones are replaced in east Dorset by micritic limestone, and at Durlston Bay, where the sequence becomes very monotonous, it is difficult to define the Member.
Definition of Lower Boundary: First significant occurrence of dark grey or brown muds above thickly bedded, ostracod-rich limestone of the Mupe Member.
Definition of Upper Boundary: Top of thicker mudstone beds beneath thick-bedded, ripple cross-laminated, quartz-detrital limestone of the overlying the Worbarrow Tout Member.
Thickness: 3 to 7m
Geographical Limits: South Dorset area, covered by British Geological Survey 1:50 000 scale Sheets 341, 342 and 343.
Parent Unit: Lulworth Formation (LULW)
Previous Name(s): Bincombe Mudstone Member (-3639)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Old quarry at Ridgeway [SY 6712 8515], near Upwey. Westhead, R K and Mather, A E, 1996. 
Reference(s):
Westhead, R K and Mather, A E. 1996. An updated lithostratigraphy of the Purbeck Limestone Group in the Dorset area. Proceedings of the Geologists' Association, Vol.107, 117-128. 
Westhead, R K. 1993. Geology of the Dorchester (south) District. British Geological Survey Technical Report, WA/93/22. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E343 E341 E342