The BGS Lexicon of Named Rock Units — Result Details

Mupe Member

Computer Code: MUP Preferred Map Code: Mup
Status Code: Full
Age range: Tithonian Age (JI) — Berriasian Age (KR)
Lithological Description: Across Dorset, in the lower part, comprises white-weathering marls and micrites containing algal laminations and some evaporitic material, with interbedded carbonaceous mudstones (caps, dirt beds) and localised brecciated limestone pockets (broken beds). Limestones, particularly in the upper part of the member (lower part of Cypris Freestones), are commonly Ostracod-rich micrites and sparites. Detrital quartz is rare. The Ostracod-rich limestones contain abundant parallel laminations and ripples, particularly higher in the member. The member may show a crude coarsening-upwards sequence, for example, at Stair Hole, Lulworth and Worbarrow Tout.
Definition of Lower Boundary: First occurrence of finely laminated, Ostracod-rich limestones above the more massive, shelly limestones of the Portland Limestone.
Definition of Upper Boundary: Last occurrence of thickly bedded, Ostracod-rich limestone (Cypris Freestones) beneath Ridgeway Member mudstones.
Thickness: 11m in west Dorset, increasing steadily to 16m in east. Anomalously thin at Stair Hole (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): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  West side of Mupe Bay (Bacon Hole), Dorset. Westhead, R K and Mather, A E, 1996. 
Reference Section  Old quarry at Upwey, Dorset. 
Westhead, R K. 1993. Geology of the Dorchester (south) District. British Geological Survey Technical Report, WA/93/22. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E341 E342 E343