| Computer Code: |
JSMU |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Norian Age (TN)
— Rhaetian Age (TR) |
| Lithological Description: |
The Joshua Mudstone Member is composed mainly of reddish brown or dark grey, slightly anhydritic silty mudstones. Stringers of white, microcrystalline limestone have been noted in well 30/12b-3. In well 30/7a-2, the Joshua Mudstone Member is represented by a thin dark grey silty mudstone. The unit is characterized by a uniform gamma-ray response and a good density/neutron separation. |
| Definition of Lower Boundary: |
The base of the Joshua Mudstone Member is defined by a downward change from mudstones to sandstones and minor mudstones (Josephine Sandstone Member). It is generally marked by a sharp downward change to more variable wireline-log signatures. |
| Definition of Upper Boundary: |
The Joshua Mudstone Member is unconformably overlain by Middle or Upper Jurassic strata in all sections, and its upper boundary marked by a sharp wireline-log break. |
| Thickness: |
The maximum recorded thickness is 25 m. |
| Geographical Limits: |
The Joshua Mudstone Member is restricted to the south Central Graben, where it is preserved in only three well sections (30/7a-2, 30/12b-3, 30/13-1) beneath the regional base-Jurassic unconformity. |
| 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 30/12b- 3: 4144.5-4168 m (13597-13675 ft) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 30/13- 1: 3740-3765.5 m (12270-12354 ft) (Cameron, 1993). |
| Reference(s): |
| 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. |
| Lott, G K, and Warrington, G. 1988. A review of the latest Triassic succession in the UK sector of the Southern North Sea Basin. Proceedings of the Yorkshire Geological Society 47, 139-147. |
| 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 |
