| Computer Code: |
HPDO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The lithofacies and thickness of the Hauptdolomit Formation were largely controlled by depositional environment, with thick shelf facies passing into a thin basinal facies. Shelf sections are composed mainly of very fine oolitic, pelletoidal, bioclastic and pisolitic grainstones, and hard, microcrystalline carbonate mudstones (e.g. 41/8-1), and locally contain a restricted fauna of bivalves, gastropods, foraminifera and ostracods. Large pisoliths and algal sheets characterize the barrier facies developed near the shelf edge. Locally, the shelf facies overlies more argillaceous slope facies and this is reflected in a downward increase in gamma-ray values (e.g. 48/22-2, Clark, 1986, fig. 19). The slope facies consist largely of dark, thinly bedded and slumped, locally argillaceous and anhydritic, dolomitized lime mudstones, together with pelleted and burrowed, structureless, argillaceous, dolomitized lime mudstones (e.g. 48/22-2, Clark, 1986, fig. 19). Lenses and beds of oolitic and bioclastic grainstones occur in both the bedded and structureless slope deposits (Clark, 1986). The thin, basin-floor facies is made up of dark, finely laminated, organic-rich, argillaceous, carbonate mudstones (e.g. 44/21-1). Coarsely crystalline limestone predominates at the centre of the basin floor, and microcrystalline dolomite around its margins. Anhydrite laminae occur up to 2 m above the base, and recur near the top of the basin-floor carbonates (Taylor, 1980). |
| Definition of Lower Boundary: |
In shelf sections, the base of the Hauptdolomit Formation is normally marked by a downward change from pale grey or pale brown dolomite to white or grey anhydrite of the Werraanhydrit Formation. It coincides with a downward increase in density and typically by a decrease in gamma-ray values (e.g. 49/26-4). In basinal sections, the base of the Hauptdolomit Formation is taken at a downward change from bituminous carbonate mudstone to interlaminated anhydrite and dolomite or limestone of the Werraanhydrit Formation. It coincides with a downward increase in density and a gradual decrease in gamma-ray values immediately below a high-gamma spike (e.g. 42/10-1 and 44/21-1 and Taylor, 1980, fig. 5). |
| Definition of Upper Boundary: |
In shelf sections, the top of the Hauptdolomit Formation is normally defined by a downward change from white to pale grey anhydrite with beds and stringers of dolomite of the Basalanhydrit Formation to pale grey to pale brown dolomite and anhydritic dolomite. It is usually marked on wireline logs by a downward decrease in density and sometimes by increase in gamma values (e.g. 41/8-1, 48/7b-4). Commonly it also coincides with a downward decrease in velocity (e.g. 41/8-1), but locally the reverse is evident (e.g. 38/16- 1 and 49/26-4). Locally, the boundary is made gradational by the interbedded nature of the dolomite/anhydrite sequence and here it is taken at the top of the dolomite-dominated section (e.g. 48/30-4).
In basinal sections, the top of the Hauptdolomit Formation is normally defined by a downward change from white, amorphous anhydrite of the Basalanhydrit Formation to dark, laminated, organic-rich dolomite. It is characterized on wireline logs by a downward decrease in density and commonly an increase in gamma-ray values and velocity. In basinal sections where the Basalanhydrit Formation is absent, the top of the Hauptdolomit Formation is marked by a downward change from halite and polyhalite of the Stassfurt Halite Formation to dark, bituminous dolomite (e.g. 47/8-1). It is marked on wireline logs by a sharp downward increase in velocity. |
| Thickness: |
Across a 10 to 40 km-wide shelf around the southern margin of the basin, the Hauptdolomit Formation is typically about 25 to 50 m thick, but locally reaches over 90 m. Thick, shelf sections are also locally present on the margins of the Mid North Sea High (e.g. 38/16-1 and 41/8-1). In the basinal sections, however, the Hauptdolomit Formation is typically about 10 to 15 m thick. |
| Geographical Limits: |
The Hauptdolomit Formation is present throughout most of the Southern North Sea. It is, however, absent from the London-Brabant Platform, which was a palaeohigh, and across the marginal platform of the Zechsteinkalk Formation, where the latter formation is directly overlain by the Basalanhydrit Formation (e.g. 53/1-1). On the Mid North Sea High, the northwestern extent of the Hauptdolomit Formation has not been encountered by drilling, but in the northern parts of quadrants 37, 38 and 39, equivalent strata are included in the Halibut Carbonate Formation (Cameron, 1993) (e.g. 38/3-1). |
| 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 41/08- 1: 917.5-1010 m (3010-3313 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 48/07b- 4: 3224-3245.5 m (10577-10648 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 49/25- 1: 2491-2541 m (8172-8737 ft) (Johnson et al., 1994). |
| Reference Section |
North Sea well 49/26- 4 (Rhys, 1974, table 2, fig.3): 1807-1855 m (5928-6086 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. |
| 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. |
| Clark, D N. 1986. The distribution of porosity in Zechstein carbonates. In: Brooks, J, Goff, J C, and Van Hoorn, B (eds.) Habitat of Palaeozoic gas in NW Europe. Geological Society, London, Special Publication No. 23, 121-149. |
| 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, 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. 1980. Origin of the Werraanhydrit in the UK Southern North Sea- a reappraisal. In: Fuchtbauer, H, and Peryt, T M (eds.) The Zechstein basin with emphasis on carbonate sequences. Contributions to Sedimentology 9, 91-113. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
