| Computer Code: |
PLDO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
In shelf sections, the Plattendolomit Formation consists dominantly of dark to pale grey or tan, hard, microcrystalline, locally argillaceous, partly pelleted and anhydritic dolomite mudstones. Thin partings of grey mudstone are common. The dolomite is locally pyritic and commonly contains secondary, soft, white, amorphous anhydrite (e.g. 48/30-3). Oolitic grainstones occur locally, particularly in the upper parts of marginal sections (e.g. 36/26-1 and 48/30-4).
The shelf facies pass basinwards into thick, slope facies consisting of dark brown, thinly bedded, unfossiliferous pyritic dolomite that contains abundant laths of replacive anhydrite (Taylor and Colter, 1975). Subordinate beds of beige or pale grey limestone are common towards the base (e.g. 49/22-3). Sporadic, thin interbeds of grey, brown or black mudstone and bituminous laminae (e.g. 41/25a-1) are present and generally more common in basal strata.
In the basin centre, the Plattendolomit Formation largely consists of white to medium grey, amorphous to cryptocrystalline anhydrite with laminations of bituminous mudstone and argillaceous dolomite (e.g. 42/10-1) and is often inseparable from the Hauptdolomit Formation (e.g. 44/11-1). |
| Definition of Lower Boundary: |
The base of the Plattendolomit Formation is normally defined by a downward change from grey microcrystalline, partly pelleted or laminated anhydritic dolomite to grey, illitic mudstone of the Grauer Salzton Formation. It is marked on wireline logs by a sharp downward increase in gamma-ray values and a decrease in velocity. Where the Grauer Salzton Formation is locally absent, the Plattendolomit Formation rests directly upon the Stassfurt Halite Formation (e.g. 49/12-3). |
| Definition of Upper Boundary: |
In most shelf and slope sections, the top of the Plattendolomit Formation is defined by a sharp downward change from white or pale grey anhydrite of the Hauptanhydrit Formation to grey microcrystalline dolomite or anhydritic dolomite. It is marked on wireline logs by a downward decrease in density, and commonly by an increase in gamma-ray values and velocity (e.g. 41/25a-1). In basinal sections (e.g. 42/10a-1) the Plattendolomit Formation commonly consists of interbedded anhydrite and dolomite, but its significantly higher argillaceous content and gamma values sometimes serve to distinguish it from the overlying Hauptanhydrit Formation. However, in some basinal sections the Plattendolomit Formation is inseparable from the Hauptanhydrit Formation (e.g. 44/11-1). Where a thin unit of halite occurs at the base of the Hauptanhydrit Formation (e.g. 48/13-2A), the top of the Plattendolomit Formation is characterized by a sharp downward increase in velocity. Where the Hauptanhydrit Formation is locally absent, the top of the Plattendolomit Formation is marked by the downward change from halite of the Leine Halite Formation to dolomite (e.g. 41/8-1).
At the extreme southern margin of the basin, the top of the Plattendolomit Formation is marked by a downward change from red-brown, or locally grey, anhydritic mudstones with minor sandstones of the Blakeney Formation to grey or tan, microcrystalline, dolomitic limestone (e.g. 53/7-2). |
| Thickness: |
From a 'feather-edge' at its southern depositional limit, the Plattendolomit Formation thickens northwards to about 90 m at a weakly developed shelf edge before thinning to about 30 m across the basin floor. Although there are few wells bordering the Mid North Sea High, a similar depositional wedge geometry appears to be developed from shelf to basin on the southwestern flank of the structure. On the southeastern flank of the Mid North Sea High, the Plattendolomit Formation passes laterally into the Turbot Anhydrite Formation, where it equates to the Turbot Carbonate unit of Cameron (1993). |
| Geographical Limits: |
The Plattendolomit Formation is widely distributed across the Southern Permian Basin. |
| 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 41/25a- 1: 1258-1302 m (4127^1272 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 42/10a- 1: 1975.5-2010.5 m (6482-6596 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 49/26- 4 (Rhys, 1974, table 2, fig. 3): 1695.5-1744.5 m (5563-5723 ft) (metric conversion revised) (Johnson et al., 1994). |
| Reference Section |
North Sea well 53/07- 2: 1513-1540 m (4964-5052 ft) (Johnson et al., 1994). |
| Reference(s): |
| 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. |
| 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. 1990. Upper Permian-Zechstein. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 153-190. Blackwell Scientific Publications, Oxford. |
| 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. |
| Richter-Bernburg, G. 1986. Zechstein salt correlation: England-Denmark-Germany. In: Harwood, G M, and Smith, D B (eds.) The English Zechstein and related topics. Geological Society, London, Special Publication No. 22, 165-168. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
