| Computer Code: |
JSSA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Norian Age (TN)
— Rhaetian Age (TR) |
| Lithological Description: |
The Josephine Sandstone Member is composed of brown and grey, generally clean, very fine, fine, or occasionally medium grained sandstone beds and minor grey, greenish grey and red siltstones and mudstones. Sorting of the sandstones is moderate or good, and many beds form discrete fining-upward units that are up to 20 m thick. Gamma-ray values for the sandstones are characteristically low. |
| Definition of Lower Boundary: |
The base of the Josephine Sandstone Member is defined by a downward change from sandstones to red and variegated silty mudstones (Jonathan Mudstone Member). It is typically marked by a sharp downward increase in gamma-ray values. Where the transition is more gradual, as at 30/1 c-5A, the boundary is taken at a sharp downward increase in density/neutron separation. |
| Definition of Upper Boundary: |
Where overlain by uppermost Triassic mudstones (Joshua Mudstone Member), the top of the Josephine Sandstone Member is typically a sharp downward transition from mudstone to sandstone (e.g. 30/12b-3). Where the sandstones are overlain by Middle or Upper Jurassic sandstones, the boundary is commonly difficult to identify from lithology alone, but can generally be recognized by a gross change in wireline-log signatures (e.g. 30/1c-5A). |
| Thickness: |
It has a maximum recorded thickness of 64 m. |
| Geographical Limits: |
The Josephine Sandstone Member is restricted to the few scattered outliers in the south Central Graben, in which it has been preserved from erosion beneath the regional base-Jurassic unconformity. The member is identifiable wherever both the overlying and underlying mudstone members are present; it passes northwards into undifferentiated Skagerrak sandstones. |
| Parent Unit: |
Skagerrak Formation (SKAG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 30/13- 1 (Deegan and Scull, 1977, p.9, fig. 13): 3765.5-3796 m (12354-12455 ft) below KB (revised base). |
| Reference Section |
North Sea well 30/01c- 5A: 4193-41233.5 m (13756-13889 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 30/12b- 3: 4168-41188.5 m (13675-13742 ft) (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. |
| 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. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
