| Computer Code: |
SULM |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Paleocene Epoch (GP)
— Paleocene Epoch (GP) |
| Lithological Description: |
The Sullom Formation is dominated by mudstone, with sandstone being restricted to marginal areas in the south and, locally, in the north (209/6-1; 208/15-1A), and to isolated basinal sections (206/1-2) (see also discussion by Ebdon et al., 1995, p.60). The mudstone ranges in colour from pale to medium green- grey to medium to dark grey. It is generally calcareous, although dark grey mudstones that occur at the base of the more complete basinal sections are commonly non- calcareous. The mudstones typically show relatively uniform wireline log characteristics, with the relatively smooth sonic log pattern commonly contrasting with the more serrated log pattern of the overlying Vaila Formation. A downward change from moderately to highly calcareous mudstone, marked by a downward increase in velocity, is displayed in some basinal sections (e.g. 208/17-1), and is associated with a marked increase in the abundance of calcareous foraminifera. |
| Definition of Lower Boundary: |
In continuous mudstone-dominated sections, the base of the Sullom Formation is taken at a sharp downward increase in gamma-ray values and decrease in velocity; in many sections, it corresponds to the top of a well defined bell-shaped gamma/sonic signature in the uppermost Jorsalfare Formation. A cored section through the boundary in well 205/10-3 shows a downward change from medium grey to brownish grey, micaceous, non-calcareous siltstone with lenses of fine sandstone (Sullom Formation) to dense medium olive-grey non-calcareous claystone (Jorsalfare Formation). The downward decrease in gamma-ray values and increase in velocity within the uppermost Jorsalfare Formation is associated with a progressive downward gradation from non-calcareous claystone to highly calcareous siltstone. |
| Definition of Upper Boundary: |
The top of the Sullom Formation is characterized by a downward change from non-calcareous mudstone associated with variable amounts of sandstone to more or less sand-free calcareous mudstone. The change to calcareous mudstones facies is associated with the downhole incoming of calcareous faunas, although these are relatively sparse in the part of the section in 208/19-1 (above c. 2870 m). The boundary is locally difficult to define in the south of the area, where sandstones are present both in the Sullom Formation and in the basal Vaila Formation. Thus in 204/19-1, the typical calcareous mudstone facies is absent, but calcareous foraminifera make a first downhole appearance within the basal sandstone unit. |
| Thickness: |
Thicknesses are highly variable, ranging up to c. 1040 m in 208/17-1. |
| Geographical Limits: |
UK north west margin. The Sullom Formation occurs in all basinal sections and in most outer shelf sections. However, it has been removed beneath the base-Faroe or base-Moray unconformities along the Rona Ridge. |
| Parent Unit: |
Shetland Group (STLN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 214/28- 1: 4535-4968 m (14878-16299 ft) (Knox et al., 1997). |
| Reference Section |
North Sea well 205/09- 1: 4568.5-4684 m (14988-15367 ft) (Knox et al., 1997). |
| Reference Section |
North Sea well 208/17- 1: 3534.5-4574 m (11596-15006 ft) (Knox et al., 1997). |
| Reference Section |
North Sea well 209/06- 1: 2372-2658 m (7782-8720 ft) (Knox et al., 1997). |
| Reference(s): |
| Knox, R W O'B, Holloway, S, Kirby, G A and Baily, H E. 1997. Stratigraphic nomenclature of the UK North West Margin. 2. Early Paleogene lithostratigraphy and sequence stratigraphy. British Geological Survey, Nottingham. |
| Ebdon, C, Granger, P J, Johnson, H D, and Evans, A M. 1995. Early Tertiary evolution and sequence stratigraphy of the Faeroe-Shetland Basin: implications for hydrocarbon prospectivity. In: Scrutton, R A, Stoker, M S, Shimmield, G B, and Tudhope, A W (eds.) The tectonics, sedimentation and palaeoceanography of the North Atlantic region. Geological Society, London, Special Publication 90, 51-69. |
| 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 |
