| Computer Code: |
HACA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The Halibut Carbonate Formation is a regionally variable unit. In many sections, it is composed of two carbonate units separated by a unit of anhydrite; in others it consists of carbonate alone (e.g. 28/5-1). The Argyll (Zl) and Innes (Z2) carbonate members are generally described as comprising light grey and pale brown dolomite and minor dolomitic limestones. However, their variable gamma-ray response (e.g. 20/2-2) suggests the presence also of sporadic laminae of mudstone or sapropelic dolomite. The Iris Anhydrite Member is almost entirely composed of white, pale pink or cream anhydrite. Thicker beds of grey, or occasionally pinkish grey or reddish brown mudstone form a significant component of the carbonate members in parts of the Moray Firth, generating irregular gammaray and sonic log motifs (Deegan and Scull, 1977). Concentrations of one or more highly radioactive mudstone beds occur towards the top of the Argyll Carbonate Member (e.g. 14/15-1) and near, or at the base of, the Innes Carbonate Member in many other areas, generating prominent gamma-ray peaks. Beds of fine to medium grained sandstone are interbedded with carbonate near the lateral transition to the Bosies Bank Formation. |
| Definition of Lower Boundary: |
The base of the Halibut Carbonate Formation is defined by a downward change from dolomite to the high-gamma mudstones of the Kupferschiefer Formation. It is generally marked by a sharp downward increase in gamma-ray values and decrease in velocity (e.g. 14/15-1), but is gradational in areas of thick Kupferschiefer development (e.g. 20/2-2). Where the Kupferschiefer Formation is locally absent, the Halibut Carbonate Formation rests unconformably on Lower Permian or pre-Permian clastic sediments (e.g. 27/10-1). |
| Definition of Upper Boundary: |
The top of the Halibut Carbonate Formation is defined by a downward change from anhydrite (Turbot Anhydrite Formation) to dolomite. In some sections (e.g. 14/4-1) the boundary is clearly gradational, being defined where carbonate replaces anhydrite as the dominant lithology. In other sections, the boundary appears from wireline-log signatures to be relatively sharp (e.g. 27/10-1). |
| Thickness: |
Thicknesses of the formation and of its constituent members vary considerably over short distances, mainly as a function of primary depositional environment. The maximum recorded thickness is 245 m in well 27/3-1. The formation is about 150 m thick in the Ettrick Field (e.g. 20/2-2), but is commonly less than 50 m thick in the Auk-Argyll area and in the centre of the Northern Permian Basin. |
| Geographical Limits: |
The Halibut Carbonate Formation extends across most areas of the Northern Permian Basin. |
| Parent Unit: |
Zechstein Group (ZG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 15/26-1 (Deegan and Scull 1977, p.7, fig.9) 3115-3131 m (10220-10272 ft) below KB. Remarks: This is a condensed section, and not now considered to be representative. Well 14/4-1 is regarded as providing a key reference section. |
| Reference Section |
North Sea well 14/04- 1: 2540.5-2607 m (8335-8553 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 14/15- 1: 2361-2393 m (7746-7851 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 20/02- 2: 3560.5-3689.5 m (11681-12105 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 27/10- 1: 1393-1493 m (4571-4898 ft) (Cameron, 1993). |
| Reference(s): |
| Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) |
| 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. |
| Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
