| Computer Code: |
SKAG |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Anisian Age (TA)
— Rhaetian Age (TR) |
| Lithological Description: |
The Skagerrak Formation in the north Central Graben, in the South Viking Graben, and in the Outer Moray Firth outliers, mostly comprises a monotonous continental red-bed sequence of fluvial sandstones and subordinate thinly bedded siltstones and mudstones. In the south Central Graben, three distinctive mudstone units interdigitate with the sandstones, enabling the Skagerrak Formation to be subdivided into six widely correlatable sandstone and mudstone members.
The relatively clean, channelized sandstones at the top of the Skagerrak Formation in the north Central Graben may be informally termed the Marnock Sandstone unit. |
| Definition of Lower Boundary: |
The base of the Skagerrak Formation is defined by a generally sharp downward change from sandstones to the monotonous silty claystones of the Smith Bank Formation, commonly marked by a sharp downward increase in gamma-ray values. However, around the crests of the largest Permian salt diapirs, the sandstones overstep the Smith Bank Formation to rest on Upper Permian evaporites.
Harker et al. (1987) considered that the base of the Skagerrak Formation is locally unconformable in the Claymore Field. |
| Definition of Upper Boundary: |
The Skagerrak Formation is everywhere overlain unconformably by Middle Jurassic, Upper Jurassic or Cretaceous strata. |
| Thickness: |
Outside the Central Graben, the thickness of the Skagerrak Formation reflects the degree of preservation beneath the regional base-Jurassic unconformity. More than 300 m of sandstones have been proved in parts of the South Viking Graben, while they are generally less than 250 m thick in the Outer Moray Firth. In the north Central Graben, the sandstones were preferentially deposited in synclines that had been developing since the early Triassic above zones of salt withdrawal in the Upper Permian evaporites (Hodgson et al., 1992). More than 300 m of Triassic sandstones have been encountered in many of these synclines, with more than 600 m proved in the Marnock Field. Only locally, as in the Kittiwake Field (Glennie and Armstrong, 1991), do thin sandstones extend over the crests of adjacent salt walls and diapirs. The sandstone and mudstone members of the Skagerrak Formation in the south Central Graben have a combined thickness of up to about 650 m. |
| Geographical Limits: |
The Skagerrak Formation is widespread across the South Viking Graben and much of the Central Graben. It also occurs as outliers in the Outer Moray Firth. The similarity of the Outer Moray Firth deposits to those in other areas suggests that the formation was formerly much more extensive before uplift and erosion caused by mid-Jurassic tectonism. |
| Parent Unit: |
Heron Group (HERO)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Norwegian North Sea well N10/8-1 (Deegan and Scull, 1977, p.9, fig. 14): 1567-2749 m (5140-9017 ft) below KB. |
| Reference Section |
North Sea well 14/19- 13: 3311.5-3641.5 m (10865-11947 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 22/05b- 3: 3078.5-3551.5 m TD (10100-11652 ft TD) (Cameron, 1993). |
| Reference Section |
North Sea well 22/24a- 1: 3535-4150 m TD (11597-13615 ft TD) (Cameron, 1993). |
| Reference Section |
North Sea well 30/12b- 3: 4144.5-4551 m (13597-14932 ft) (Cameron, 1993). |
| Reference(s): |
| Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic 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. |
| 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. |
| 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.) |
| Andrews, I J, Long, D, Richards, P C, Thomson, A R, Brown, S, Chesher, J A, and McCormac, M. 1990. The geology of the Moray Firth. (London: British Geological Survey.) |
| Fisher, M J, and Mudge, D C. 1990. Triassic. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 191-218. Blackwell Scientific Publications, Oxford. |
| Harker, S D, Gustav, S H and Riley, L A. 1987. Triassic to Cenomanian stratigraphy of ther Witch Ground Graben. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 809-818. [Graham & Trotman, London] |
| Glennie, K W, and Armstrong, L A. 1991. The Kittiwake Field, Block 21/18, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields 25 years commemorative volume. Geological Society, London, Memoir No. 14, 339-345. |
| Goldsmith, P J, Rich, B, and Standring, J. 1995. Triassic correlation and stratigraphy in the South Central Graben, United Kingdom North Sea. In: Boldy, S A R (ed.) Permian and Triassic rifting in NW Europe. Geological Society, London, Special Publication. |
| Hodgson, N A, Farnsworth, J, and Fraser, A J. 1992. Salt-related tectonics, sedimentation and hydrocarbon plays in the Central Graben, North Sea, UKCS. In: Hardman, R F P (ed.) Exploration Britain: Geological insights for the next decade. Geological Society, London, Special Publication No.67, 31-63. |
| Spark, I S C, and Trewin, N H. 1986. Facies-related diagenesis in the main Claymore Oilfield sandstones. Clay Minerals 21, 479-496. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
