| Computer Code: |
STHA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The Stassfurt Halite Formation has not generally been cored in the Southern North Sea and lithological information is therefore based largely on drill cuttings, wireline log evidence and analogy with equivalent cored successions in eastern England (e.g. Colter and Reed, 1980). The Stassfurt Halite Formation consists of halite with subordinate interbedded anhydrite, polyhalite and kieserite. Minor amounts of carnallite are also present near the top of the formation. The halite is generally coarsely crystalline, transparent to translucent, locally coloured orange or pink, and occasionally white and opaque. The anhydrite is interbedded and intergrown with the halite and is generally white and amorphous to microcrystalline. The beds of polyhalite are white to pale grey, occasionally brick red, pink and orange, and amorphous to microcrystalline. A thin unit (usually about 1 m thick) of white to pale grey anhydrite (Deckanhydrit) commonly caps the formation. Where seen in cores, it consists of spindle-shaped microcrystalline anhydrite crystals aligned with the bedding. |
| Definition of Lower Boundary: |
Near basin margins, the base of the Stassfurt Halite Formation is taken at a downward change from dominantly halite to pale grey anhydrite of the Basalanhydrit Formation. It is marked on wireline logs by a sharp downward increase in velocity (e.g. 49/26-4). In many basinal sections, the Basalanhydrit Formation is absent and the base of the Stassfurt Halite Formation is marked by a downward change from interbedded anhydrite and polyhalite to dark grey dolomite or dolomitic limestone of the Hauptdolomit Formation (e.g. 44/11-1 and 47/8-1). The associated changes in wireline log character are somewhat variable, depending upon whether a widespread polyhalite-rich section, characterized by many, high gamma-ray spikes, is at or near the base of the Stassfurt Halite Formation. |
| Definition of Upper Boundary: |
The top of the Stassfurt Halite Formation is normally defined by a downward change from pale grey to grey, illitic, unfossiliferous marine mudstones of the Grauer Salzton Formation to anhydrite-capped (Deckanhydrit) halite with subordinate anhydrite, polyhalite, kieserite and carnallite. It is marked on wireline logs by a sharp downward decrease in gamma-ray values and an increase in velocity. Locally, the Deckanhydrit is absent and the Grauer Salzton Formation rests directly on halite (e.g. 44/11-1). Where the Grauer Salzton Formation is absent, grey dolomite or anhydrite of the Plattendolomit Formation rests directly on the Stassfurt Halite Formation (e.g. 43/26-5). |
| Thickness: |
The Stassfurt Halite Formation may have been over 500 m thick in the centre of the basin, but depostional thicknesses in this area are difficult to estimate because of the extensive deformation by halokinesis (Cameron et al., 1992). Where the Stassfurt Halite Formation overlies the slope and adjacent basin-floor facies of the Basalanhydrit and Hauptdolomit formations, it is about 250 m thick, but thins rapidly onto the shelf (e.g. 49/22-3). At the basin margins, the Stassfurt Halite Formation passes laterally into red mudstones of the Blakeney Formation. |
| Geographical Limits: |
The Stassfurt Halite Formation is present over much of the Southern North Sea Basin. It is absent from the Mid North Sea High, although it passes laterally into thick halites and anhydrites of the Shearwater Evaporite Formation in a north-trending, trough-like feature in quadrant 37 (Jenyon et al., 1984) (e.g. 37/12-1). According to Taylor (1991), Z2 evaporites may have originally been far more extensive over the Mid North Sea High, having been removed by dissolution beneath thick overburden. In the central parts of the Southern North Sea, where sections have been extensively disrupted by halokinesis, the Stassfurt Halite Formation passes laterally into undivided Zechstein salts. |
| 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 44/11- 1: 2747-3360 m (9012-11024 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 47/08- 1: 2362-2771 m (7750-9091 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 48/13- 2A: 2079.5-2375.5 m (6822-7794 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 49/26- 4: 1745.5-1772 m (5727-5813 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. 1993. 4. Triassic, Permian and pre-Permian of the Central and Northern 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.) |
| Jenyon, M K, Cresswell, P M, and Taylor, J C M. 1984. Nature of the connection between the Northern and Southern Zechstein basins across the Mid North Sea High. Marine and Petroleum Geology 1, 355-363. |
| 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, 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. |
| Taylor, J C M. 1990. Upper Permian-Zechstein. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 153-190. Blackwell Scientific Publications, Oxford. |
| Colter, V S, and Reed, G E. 1980. Zechstein 2 Fordon Evaporites of the Altwick No. 1 borehole, surrounding areas of NE England and the adjacent southern North Sea. In: Fuchtbauer, H, and Peryt, T M (eds.) The Zechstein Basin with emphasis on carbonate sequences. Contributions to Sedimentology 9, 115-129. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
