| Computer Code: |
JUMU |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Anisian Age (TA)
— Ladinian Age (TD) |
| Lithological Description: |
The Julius Mudstone Member is composed of grey, brownish grey, greenish grey and occasionally reddish brown, patchily anhydritic silty mudstones, with sporadic partings of argillaceous limestone and microcrystalline dolomite. The mudstones display average gamma-ray values lower than those of the overlying and underlying sandstone members, possibly because of a lower mica content or a higher proportion of carbonate, and are best identified by their wide neutron-density log separation. They generate characteristic convex bow-shaped sonic, resistivity and density log responses, and a concave bowshaped gamma-log response (Goldsmith et al., 1995). The characteristic log features are largely restricted to wells in Quadrant 30 (e.g. 30/12b-3; 30/lc-5A). Further west and north, the mudstone that overlies the basal Skagerrak sandstone unit displays a convex bowshaped gamma-ray response, and can only be tentatively equated with the Julius Mudstone Member (e.g. 29/8a-3; 29/19-1 A, p.49; 22/24b-9). |
| Definition of Lower Boundary: |
The base of the Julius Mudstone Member is defined by a downward change from silty mudstone to sandstone with minor mudstone (Judy Sandstone Member). Where the member is thickest, the contact is often gradational. It is marked by a downward decrease in velocity and density. |
| Definition of Upper Boundary: |
The top of the Julius Mudstone Member is defined by a gradational downward change from sandstones with minor mudstones (Joanne Sandstone Member) to silty mudstones. It is marked by a generally sharp downward increase in velocity, resistivity and density. |
| Thickness: |
The proven thickness of the member varies between about 20 m and 150 m (Goldsmith et al., 1995). |
| Geographical Limits: |
The Julius Mudstone Member is largely confined to Triassic basins in Quadrant 30, though the high-gamma mudstone unit that occurs above the basal Skagerrak sandstone in parts of Quadrant 29 may be laterally equivalent. |
| 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: 4422-4457 m (14507-14622 ft) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 30/07a- 3: 4129-4216 m (13546-13832 ft) (Cameron, 1993). |
| Reference(s): |
| Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. The geology of the southern North Sea. United Kingdom offshore regional report. (London: HMSO for the British Geological Survey.) |
| 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. |
| 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 |
