| Computer Code: |
MORG |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The Morag Member is generally composed of white, pale grey, or occasionally pinkish grey anhydrite, with minor partings and thin beds of reddish brown, pale brown, and greenish grey mudstone (e.g. 21/18-2A, 28/12-1). The anhydrite is variously described from cuttings as being amorphous, cryptocrystalline, microcrystalline or sucrosic. Patches of halite have been recorded locally. |
| Definition of Lower Boundary: |
The base of the Morag Member is defined by a downward change from anhydrite to salts of the Shearwater Salt Formation. It is marked by a sharp downward decrease in velocity, but where mudstone is present at the base of the member (e.g. 29/27-1) is associated with a sharp downward increase in velocity. |
| Definition of Upper Boundary: |
The Morag Member is mostly overlain by basal Triassic silty mudstones of the Smith Bank Formation, where the boundary is defined by a sharp downward change from mudstone to anhydrite or dolomite and marked by a sharp downward decrease in gamma-ray values and increase in velocity. It subcrops Jurassic or younger rocks in some areas of deep Mesozoic erosion. |
| Thickness: |
The member is generally more than 30 m thick, but locally up to 200 m thick in central parts of the Central Graben and South Viking Graben. |
| Geographical Limits: |
The Morag Member can be distinguished on wireline logs only where the anhydrite is more than 5 m thick; it is thin or absent above salts in parts of Quadrant 30 and in the South Halibut Basin. The member is otherwise widespread across central parts of the Northern Permian Basin. |
| Parent Unit: |
Turbot Anhydrite Formation (TBAN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
North Sea well 21/18- 2A: 3109.5-3202.5 m (10202-10507 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 28/12- 1: 1166-1214 m (3825-3983 ft) (Cameron, 1993). |
| Reference(s): |
| 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. |
| Taylor, J C M. 1990. Upper Permian-Zechstein. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 153-190. Blackwell Scientific Publications, Oxford. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
