| Computer Code: |
INCA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The Innes Carbonate Member is largely composed of white, grey, or pale brown, microcrystalline or sucrosic dolomite and minor limestone. The basal carbonates are argillaceous, and are interbedded with grey, or occasionally pinkish grey to reddish brown mudstones. The latter form beds that are up to 10 m thick in parts of the Moray Firth, where mudstone is locally the principal lithology. The uppermost carbonates are commonly anhydritic. The carbonate member generates a distinctive 'upward-cleaning' gamma-ray profile in many sections. |
| Definition of Lower Boundary: |
Where the Innes Carbonate Member overlies the Iris Anhydrite Member, the boundary is defined by a rapid downward transition from argillaceous dolomite or mudstone to anhydrite. It is marked by a sharp downward decrease in gamma-ray values, accompanied by an increase in velocity and resistivity.
In many basin-margin sections, the Iris Anhydrite Member is absent, and the Innes Carbonate Member lies directly, and possibly disconformably, on the Argyll Carbonate Member. In such sections, the boundary may not be easily distinguished, although many sections display a downward change from higher-gamma, argillaceous dolomites to cleaner dolomites (e.g. 20/2-2). A superficially similar succession occurs in many basinal sections, where the Argyll Carbonate Member extends upwards to include equivalents of the Iris Anhydrite Member. In such sections, however, the boundary is clearly defined by a downward transition from argillaceous to clean anhydritic dolomites, and is generally marked by a sharp downward decrease in gamma-ray values, and increase in velocity and resistivity (e.g. 21/11-1). |
| Definition of Upper Boundary: |
The top of the Innes Carbonate Member is defined by a downward change from anhydrite-dominated lithologies (Turbot Anhydrite Formation) to dolomite-dominated lithologies. On wireline logs, the boundary appears sharp (e.g. 27/10-1) or transitional (e.g. 14/4-1). In well 27/3-1, the Innes Carbonate Member is directly overlain by the (Z3) Turbot Carbonate unit. The Z2/Z3 boundary was tentatively placed by Taylor (1990) at a downhole change from limestone to dolomite. |
| Thickness: |
The member may be up to 70 m thick in the west of the Ettrick Field, where its base is poorly defined, but it is typically less than 20 m thick. |
| Geographical Limits: |
The Innes Carbonate Member extends across most parts of the Central North Sea and South Viking Graben, but is not differentiated north of 60°N, where few wells penetrate the Halibut Carbonate Formation. In some basinal areas, the member is either absent or too thin to be resolved (e.g. 14/20-2). It is also absent locally as a result of Mesozoic erosion. |
| Parent Unit: |
Halibut Carbonate Formation (HACA)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 30/23a- 3: 2691.5-2701.5 m (8830-8863 ft) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 20/03- 3: 3723-3755 m (12214-12320 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 21/11- 1: 3134-3145 m (10283-10319 ft) (Cameron, 1993). |
| 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. |
| Bifani, R. 1985. A Zechstein depositional model for the Argyll field. 11-118 in The role of evaporites in hydrocarbon exploration. Taylor, J C M et al. (editors). JAPEC Course Notes No. 39. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
