| Computer Code: |
RONA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Bajocian Age (JB)
— Tithonian Age (JI) |
| Lithological Description: |
The Rona Formation comprises a thin succession of sandstones, conglomerates, mudstones and siltstones. Detailed studies of core from this formation have identified 5 clastic-dominated facies within a generally simple fining upward succession (Vestralen and Hurst, 1994; Vestralen et al., 1995). They refer to facies 1 to 3 as the 'Rona Sandstone' (facies 1 is the oldest) and facies 4 to 5 as the 'Rona Siltstone'.
Facies 1: Thin (average l m), matrix-supported, poorly sorted, angular conglomerates and fine- to coarse-grained, carbonate cemented sandstones.
Facies 2: Thin (average 0.45 m), fine to coarse-grained, poorly sorted, massive to stratified, pebbly, carbonate cemented, occasionally shelly sandstones.
Facies 3: Fine- to coarse-grained, poorly sorted, massive, carbonate cemented, very shelly sandstones with thin carbonaceous mudstones.
Facies 4: Planar, parallel-laminated, carbonaceous, shelly, carbonate cemented siltstones.
Facies 5: Planar, parallel-laminated, carbonaceous, shelly, occasionally bioturbated siltstones and mudstones with thin, interbedded, fine-grained sandstones. |
| Definition of Lower Boundary: |
The Rona Formation commonly rests with a marked unconformity on Lewisian gneisses, but occasionally on Foula Formation sandstones (e.g. 205/25-1) or Sule Skerry Formation mudstones (e.g. 202/3a-3). On wireline logs, the boundary between the Rona Formation sandstones and the Lewisian gneisses or Foula Formation sandstones is generally marked by a downward decrease in gamma-ray log values and an increase in velocity. In contrast, the transition between the Rona Formation and Sule Skerry Formation is marked by a sharp downward increase in gamma-ray log values and a decrease in velocity. |
| Definition of Upper Boundary: |
The top of the Rona Formation is usually marked by a downward change from Kimmeridge Clay Formation non-calcareous mudstones, to sandstones, siltstones and mudstones. This transition is represented on wireline logs by a downward decrease in the gamma-ray log values and an increase in velocity. |
| Thickness: |
A maximum drilled thickness of 82 m has been recorded from well 202/3-1A in the North Rona Basin. |
| Geographical Limits: |
The Rona Formation is present within the North Rona, Solan and West Shetland basins, on the Westray Ridge and along the southeast margin of the Faeroe-Shetland Basin. |
| Parent Unit: |
Humber Group (HMBG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 202/03- 1A: 1637-1719 m (5371-5640 ft) (Ritchie et al., 1996). |
| Reference Section |
North Sea well 204/28- 1: 1872-1940 m (6142-6365 ft) (Ritchie et al., 1996). |
| Reference(s): |
| Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) |
| 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. |
| Vestralen, I, Hartley, A J, and Hurst, A. 1995. The sedimentology of the Rona Sandstone (Upper Jurassic), West Shetland Basin, UK. In: Hartley, A J, and Prosser, D J (eds.) Special Publication of the Geological Society of London, No. 55, 155-176. |
| Vestralen, I, and Hurst, A. 1994. Sedimentology, Reservoir Characteristics and Exploration Potential of the Rona Sandstone (Upper Jurassic), West of Shetland UKCS. First Break, 12, 11 -20. |
| 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 |
