| Computer Code: |
ROSO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Aptian Age (KP)
— Albian Age (KA) |
| Lithological Description: |
The Royal Sovereign Formation consists of conglomerates and marine sandstones with interbedded mudstones. It includes a lower unit of grey and dark grey to greenish sandy conglomerates and breccias containing basement lithologies including quartzite, schist and granite, in addition to pebbles of shale and siltstone. The matrix may be fine grained or poorly sorted fine to coarse sandstone, and includes glauconite and comminuted shell fragments (Meadows et al., 1987). Porosities are very low and the formation has a high sonic velocity and an irregular gamma-ray response. The conglomerates are locally calcareous and pyritic. Interbedded sandstones and dark grey mudstones are rare. Above the conglomeratic unit is a succession of medium- to fine-grained, locally coarse and pebbly sandstones interbedded with mudstones. Individual sandstones are generally thin (<5 m), but may thicken up to about 20 m. Bases of sandstone units are sharp with abrupt downward increases in gamma-ray values. The mudstones are grey to very dark grey, occasionally laminated, pyritic, and generally not calcareous. |
| Definition of Lower Boundary: |
The type well is the only location where the base of the Royal Sovereign Formation is reached, and the conglomerates rest directly on metamorphic basement. The sonic velocity in the conglomerates is high, and there is no marked increase at the unconformity, which is marked by a reduction in gamma-ray values. |
| Definition of Upper Boundary: |
The top of the Royal Sovereign Formation is marked by a sharp decrease in gamma-ray values and an increase in sonic velocities, marking the downward change from the mudstones of the Cruiser Formation into interbedded sandstones and mudstones. A few thin sandstones may occur within the Cruiser Formation, and the top of the Royal Sovereign Formation is taken at the top of the first thicker sandstone, marked by a more continuous change to an increase in sonic velocity and a lower gamma-log response. |
| Thickness: |
In well 206/3-1 it reaches a thickness of more than 401.5 m. Continuity of the formation between this well and 208/26-1 is not proven. In well 206/5-1 sediments of the same age are probably absent, and there are no other wells in the northern part of the Faeroe-Shetland Basin that penetrate the base of the overlying Cruiser Formation. The Royal Sovereign Formation is absent on the Erlend Terrace. In the southern part of the Faeroe-Shetland Basin, the absence of the formation in 205/16-1 and 205/22-1 limits its distribution. Well 206/11-1 bottoms in 124 m of conglomerates that are assigned to the Royal Sovereign Formation. They are directly overlain by only 25 m of mudstones assigned to the Cruiser Formation.
Above this thin mudstone, a succession nearly 1000 m thick, predominantly of sandstones, extends up into the Cenomanian. They are here assigned to the Commodore Formation. Further work in this area may require modification of the scheme proposed here, to clearly separate the Royal Sovereign and Commodore formations if the Cruiser Formation is locally proved thin or absent. |
| Geographical Limits: |
The Royal Sovereign Formation is restricted to the Faeroe-Shetland Basin to the west of the Rona Ridge. |
| Parent Unit: |
Cromer Knoll Group (CRKN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 208/26- 1: 3681.5-3875 m (12078-12713 ft) (Ritchie et al., 1996). |
| Reference Section |
North Sea well 206/03- 1: 4542.5-4944 m (TD) (14903-16220 ft TD) (Ritchie et al., 1996). |
| Reference(s): |
| Meadows, N S, Macchi, L, Cubitt, J M, and Johnson, B. 1987. Sedimentology and reservoir potential in the West of Shetland area, UK exploration area. In: Brooks, J, and Glennie, K W (eds.) Petroleum Geology of North-West Europe. (London: Graham and Trotman), 723-736. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
