| Computer Code: |
JRSF |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Campanian Age (KC)
— Maastrichtian Age (KM) |
| Lithological Description: |
The Jorsalfare Formation consists of mudstones with interbedded argillaceous chalky limestones. The mudstones are pale grey to grey and usually calcareous. The limestones are argillaceous, chalky, white to pale grey, but locally red brown, fine grained and occasionally sandy and dolomitic. In the East Shetland Basin, the proportion of limestone relative to mudstone generally decreases to the north and east. |
| Definition of Lower Boundary: |
The base of the Jorsalfare Formation is normally characterized by a downward change from argillaceous chalky limestones and calcareous mudstones, which are characteristically red brown, to grey mudstones of the Kyrre Formation. On wireline logs it corresponds to a downward increase in gamma values and a decrease in velocity. |
| Definition of Upper Boundary: |
In the Beryl Embayment, North Viking Graben and East Shetland Basin, the top of the Jorsalfare Formation is usually marked by a downward passage from calcareous mudstones of the Maureen Formation to increasingly calcareous mudstones (e.g. 211/13-7, 3/12-2). On wireline logs it is marked by a downward increase in velocity. In some sections the basal mudstones of the Maureen Formation are replaced by thinly bedded sandstone or reworked limestone (e.g. 9/19-7Z). In such cases the boundary is usually marked by a downward change from more variable to more consistent gamma and sonic responses. Where relatively pure reworked limestone rests unconformably on calcareous mudstones of the Jorsalfare Formation (e.g. 3/29-1) a downward increase in gamma values and a decrease in velocity is recorded.
In the South Viking Graben, the top of the Jorsalfare Formation is normally characterized by a downward change from argillaceous chalky limestones and interbedded calcareous mudstones of the Ekofisk Formation to cleaner limestones. It is marked by a downward decrease in gamma values and an increase in velocity (e.g. 16/3a-1). |
| Thickness: |
In contrast to the underlying formations of the Shetland Group, the Jorsalfare Formation displays only minor lateral thickness variation, and forms a blanket-like layer generally about 300-400 m thick (Johnson et al., 1993). |
| Geographical Limits: |
The Jorsalfare Formation is widely distributed in the Viking Graben, Beryl Embayment and East Shetland Basin. |
| Parent Unit: |
Shetland Group (STLN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Norwegian Sector North Sea well N25/1-1 (Isaksen and Tonstad, 1989, p.30, fig.33): 2711-2997 m (8894-9832.5 ft) below KB. |
| Reference Section |
North Sea well 3/12- 2: 2134-2448.5 m (7002-8033 ft) (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 3/29- 1: 2628-2925 m (8622-9596 ft) (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 16/3a- 1: 2847-3251.5 m (9340-10668 ft) (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 211/13- 7: 1809.5-2126 m (5936-6975 ft) (Johnson and Lott, 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. |
| Isaksen, D and Tonstad, K. 1989. A revised Cretaceous and Tertiary lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No.5 |
| Johnson, H, Richards, P C, Long, D, and Graham, C C. 1993. United Kingdom offshore regional report: the geology of the northern North Sea. (London: HMSO for the British Geological Survey.) |
| King, C, Bailey, H W, Burton, C A, and King, A D. 1989. Cretaceous of the North Sea. In: Jenkins, D G and Murray, J W (eds) Stratigraphical atlas of fossil foraminifera, 372-417. Ellis Horwood Limited, Chichester, for the British Micropalaeontological Society. |
| Abbotts, I L (ed.) 1991. United Kingdom oil and gas fields 25 years commemorative volume. Geological Society, London, Memoir No. 14. |
| 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.) |
| Ritchie, J D, Gatliff, R W and Riding, J, 1996. 1. Pre - Tertiary lithostratigraphy. In: Stratigraphic Nomenclature of the UK North West Margin. British Geological Survey, Nottingham. |
| Johnson, H and Lott, G K. 1993. 2. Cretaceous 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
