The BGS Lexicon of Named Rock Units — Result Details

Grauer Salzton Formation

Computer Code: GRSA Preferred Map Code: notEntered
Status Code: Full
Age range: Guadalupian Epoch (PUG) — Lopingian Epoch (PUL)
Lithological Description: The Grauer Salzton Formation consists of pale to dark grey, locally black and laminated, illitic, unfossiliferous mudstones. Chlorite and kaolinite and subsidiary minerals in the mudstones (Taylor and Colter, 1975), which are usually described on composite logs as soft and sticky. Locally the mudstones are silty (e.g. 48/7b-4) or dolomitic and marly with secondary, white, amorphous, soft anhydrite (e.g. 47/15-1). Although the Grauer Salzton Formation is generally thin, various gamma-ray and velocity log signatures are recorded, including a simple high gamma-ray / low velocity spike, upward-increasing gamma values (e.g. 47/15-1), upward-decreasing gamma values (e.g. 42/10-1) and erratic gamma values (e.g. 49/17-1).
Definition of Lower Boundary: The base of the Grauer Salzton Formation is normally defined by a downward change from pale to dark grey, illitic mudstone to anhydrite-capped (Deckanhydrit) halite of the Stassfurt Halite Formation (e.g. 36/26-1). It is marked on wireline logs by a downward decrease in gamma-ray values and an increase in velocity. Where the Deckanhydrit is absent, the Grauer Salzton Formation rests directly on halite or interbedded halite, anhydrite, polyhalite, carnallite and kieserite of the Stassfurt Halite Formation. At the southern basin margin, the Grauer Salzton Formation locally rests on anhydritic red-brown mudstones of the Blakeney Formation (e.g. 53/1-2). This boundary is marked by a downward decrease in gamma-ray values and an increase in velocity.
Definition of Upper Boundary: In sections around the basin margins, the top of the Grauer Salzton Formation is normally defined by a downward change from grey, microcrystalline, partly pelleted or laminated anhydritic dolomite of the Plattendolomit Formation to grey mudstone. It is typically marked on wireline logs by a sharp downward increase in gamma-ray values and a decrease in velocity. In the basin centre, the Grauer Salzton Formation is overlain by white to grey, amorphous or microcrystalline anhydrite with bands of dolomite of the Plattendolomit Formation (e.g. 42/10-1) or anhydrite of the Plattendolomit/Hauptdolomit formations (e.g. 44/11-1). This boundary is also marked by a downward increase in gamma-ray values and a decrease in velocity.
Thickness: The Grauer Salzton Formation is typically 1 to 3 m thick, but locally reaches over 7 m (e.g. 47/15-1).
Geographical Limits: The Grauer Salzton Formation is present throughout much of the Southern North Sea Basin. It is, however, absent from the Mid North Sea High and the South Hewett Shelf/London-Brabant Platform. It is also locally absent in the basinal areas due to local halokinesis which has disturbed the normal stratigraphic succession.
Parent Unit: Zechstein Group (ZG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  North Sea well 47/15- 1: 2425.5-2431 m (7958-7975 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 49/26- 4 (Rhys, 1974, table 2, fig. 3): 1744.5-1745.5 m (5723-5727 ft) (revised depths) (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. 
NAM and RGD (Nederlandse Ardolie Maatschappij and Rijks Geologische Dienst) 1980. Stratigraphic nomenclature of the Netherlands. Transactions of the Royal Dutch Geological and Mining Society of Delft. 
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. 
Smith, D B. 1980. The evolution of the English Zechstein basin. In: Fuchtbauer, H, and Peryt, T M (eds.) The Zechstein basin with emphasis on carbonate sequences. Contributions to Sedimentology 9, 7-34. 
Smith, D B. 1989. The late Permian palaeogeography of north-east England. Proceedings of the Yorkshire Geological Society, Vol.47, 285-312. 
Smith, D B, Brunstrom, R G W, Manning, D I, Simpson, S and Shotton, F W. 1974. A correlation of Permian rocks in the British Isles. Geological Society of London Special Report No. 5. 
Smith, D B, Harwood, G M, Pattison, J and Pettigrew, T H. 1986. A revised nomenclature for Upper Permian strata in eastern England. 9-17 in Harwood, G M and Smith, D B (editors). The English Zechstein and Related Topics. Geological Society Special Publication No.22. 
Taylor, J C M, and Coulter, V S. 1975. Zechstein of the English sector of the Southern North Sea. In: Woodland, A W (ed.) Petroleum and the continental shelf of North-West Europe, 249-263. Applied Science Publishers, London. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable