The BGS Lexicon of Named Rock Units — Result Details

Bröckelschiefer Member

Computer Code: BSR Preferred Map Code: Bsr
Status Code: Full
Age range: Early Triassic Epoch (TE) — Early Triassic Epoch (TE)
Lithological Description: The Bröckelschiefer Member comprises red-brown to chocolate brown, micaceous, calcareous (dolomitic) or anhydritic shales, silty mudstones and siltstones with some interbeds of very fine to fine, red-brown sandstone. The member is commonly upward-fining in character, indicated by an upward-increasing gamma-ray profile, and has a distinctly higher velocity than the overlying Bunter Shale Formation mudstones. Thicker sandstones, including the Hewett Sandstone, a reservoir unit for the Hewett Field (Cumming and Wyndham, 1975), are developed in the southern part of the basin, adjacent to the London-Brabant Platform.
Definition of Lower Boundary: The base of the Bröckelschiefer Member corresponds to the base of the Bunter Shale Formation. Within the limits of the former Permian evaporite basin in the UK sector the base of the member is defined by a sharp downward change from red-brown silty mudstones and siltstones with sandstone interbeds to evaporites and evaporitic mudstones of the Zechstein Group; a marked downward decrease in gamma-ray values and an increase in velocity occur at this level. To the south of the former evaporite basin, the boundary is commonly less clear and is open to different interpretations, including the possibility that the member oversteps beds of the Z4 sequence and rests unconformably upon older (Z3) beds of the Zechstein Group.
Definition of Upper Boundary: The top of the Bröckelschiefer Member is placed at a downward change from red silty mudstones to red-brown silty mudstones and siltstones with sandstone interbeds; this is marked by a downward decrease in gamma-ray values and an increase in velocity. Locally, the top of the Hewett Sandstone corresponds with the top of the member.
Thickness: The member varies from 20 m up to 70 m in thickness (Cameron et al., 1992). The Hewett Sandstone has a maximum thickness of over 60 m and is restricted to the area of the South Hewett Shelf, adjacent to the London-Brabant Platform (Cumming and Wyndham, 1975; Cameron et al., 1992).
Geographical Limits: The Bröckelschiefer Member is coextensive with the Bunter Shale Formation within the Southern North Sea region.
Parent Unit: Bunter Shale Formation (BTSH)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 49/21- 2 (Rhys, 1974): 1983-2011 m (6505-6597 ft) below KB. 
Reference Section  North Sea well 42/10a- 1: 1625.5-1639 m (5333-5378 ft) (Johnson et al., 1994). 
Reference(s):
Johnson, H, Warrington, G and Stoker, S J. 1994. 6. Permian and Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. The geology of the southern North Sea. United Kingdom offshore regional report. (London: HMSO for the British Geological Survey.) 
Fisher, M J, and Mudge, D C. 1990. Triassic. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 191-218. Blackwell Scientific Publications, Oxford. 
Geiger, M E, and Hopping, C A. 1968. Triassic stratigraphy of the southern North Sea Basin. Philosophical Transactions of the Royal Society of London B254, 1-36. 
Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. 
Cumming, A D, and Wyndham, C L. 1975. The geology and development of the Hewett gas-field. In: Woodland, A W (ed.) Petroleum and the continental shelf of north-west Europe, 313-325. Applied Science Publishers, London. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E162