| Computer Code: |
AUK |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Cisuralian Epoch (PLC)
— Lopingian Epoch (PUL) |
| Lithological Description: |
Reddish brown or grey aeolian sandstones constitute most of the Auk Formation in the Argyll Field (Bifani et al., 1987), Auk Field (Heward, 1991), Innes Field (Robson, 1991), and across much of the Central North Sea (Glennie, 1990). Normally the sandstones are cemented by hematite and authigenic clay, but dolomite and anhydrite are locally important cements (Deegan and Scull, 1977), as is kaolinite (Trewin and Bramwell, 1991). Locally the uppermost few metres of sandstone have been tightly cemented by porewaters that percolated from overlying Upper Permian strata. |
| Definition of Lower Boundary: |
In much of the Central North Sea and in the South Viking Graben, the Auk Formation rests unconformably on Devonian strata of comparable red-bed facies, and the boundary is consequently difficult to identify. The few wells to have penetrated the Permian/Devonian boundary (e.g. 30/16-9), indicate that it can be defined by a sharp downward increase in gamma-ray values, velocity, and resistivity. In well 30/16-1 (Auk Field), the boundary was placed at the base of a high-velocity basal conglomerate of the Auk Formation by Deegan and Scull (1977, p.5, fig.4); comparable conglomerates have not been reported elsewhere. |
| Definition of Upper Boundary: |
In most sections, the top of the Auk Formation is defined by a sharp downward change from highly radioactive mudstones of the Kupferschiefer Formation, or from carbonates of the Halibut Carbonate Formation, to sandstones. In the east of the Auk Field and in other areas that suffered deep erosion during Mesozoic uplift, the formation is overlain by Upper Jurassic or Cretaceous rocks. |
| Thickness: |
Glennie (1990) noted that thickness variation of the Auk Formation has been caused largely by relief on its basal unconformity. In the Auk Field and in a few other areas of Mesozoic uplift and deep erosion, part of the variation is due to truncation beneath Jurassic or Cretaceous strata.
In the Auk Field (Block 30/16), the Auk Formation comprises a wedgeshaped accumulation that thins across the field from 500 m to 150 m as it onlaps gently tilted Devonian strata (Heward, 1991). Deposition of Lower Permian sands in the Argyll Field (Block 30/24) was limited to central areas by topography on the base-Permian unconformity (Robson, 1991); in these areas, the Auk Formation is less than 60 m thick. Limited well data indicate that Lower Permian sandstones are likely to be generally over 150 m thick elsewhere in the Central North Sea and South Viking Graben. |
| Geographical Limits: |
The Auk Formation is widespread in the Central North Sea, except in Quadrants 20 and 21, where it is largely absent. It occurs in the South Viking Graben, and extends into parts of the Outer Moray Firth. Few wells have penetrated as deep as the Permian in the East Shetland Basin, but those that have indicate that the formation is absent from the Magnus Embayment. |
| Parent Unit: |
Rotliegend Group (RLG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 30/16- 1 (Deegan and Scull, 1977, p.5, fig.4): 2375-2859 m (7792-9380 ft) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 9/28- 2: 2761-2981.5 m TD (9058-9782 ft TD) (Cameron, 1993). |
| Reference Section |
North Sea well 30/16- 9: 2356-2628 m (7730-8622 ft). The Lower Permian interval in 30/16-9 provides a better illustration than in the type well of the gamma-ray, velocity and resistivity contrasts that distinguish the Auk Formation from subcropping Devonian strata (Cameron, 1993). |
| Reference(s): |
| 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. |
| Glennie, K W. 1990. Lower Permian - Rotliegend. In: Glennie, K W (ed.) Introduction to the Petroleum Geology of the North Sea, Blackwell Scientific Publications, p. 120 - 152. |
| Robson, D. 1992. The Argyll, Duncan and Innes fields, Blocks 30/24 and 30/25a, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields, 25 years commemorative volume. Memoir of the Geological Society, London, 14, 219-225. |
| Trewin, N H, and Bramwell, M G. 1991. The Auk Field, Block 30/16, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields 25 years commemorative volume, Geological Society, London, Memoir No. 14, 227-236. |
| Yaliz, A. 1991. The Crawford Field, Block 9/28a, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields 25 years commemorative volume. Geological Society, London, Memoir No. 14, 287-293. |
| Bifani, R, George, G T, and Lever, A. 1987. Geological and reservoir characteristics of the Rotliegend sandstones in the Argyll Field. 509-522 in Petroleum geology of North West Europe. Brooks, J, and Glennie, K W (editors). (Graham and Trotman, London.) |
| Heward, A P. 1991. Inside Auk - the anatomy of an eolian oil reservoir. In: Miall, D, and Tyler, N (eds.) The three-dimensional facies architecture of clastic sediments and its implications for hydrocarbon discovery and recovery, 44-56. Society of Economic Paleontologists and Mineralogists. |
| 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. |
| 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.) |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
