| Computer Code: |
TOVO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Asselian Age (PA)
— Asselian Age (PA) |
| Lithological Description: |
In 110/2b-10, the Tormentil Volcanics consist of interbedded basalts and basaltic andesites, but possibly include an overlying ?volcaniclastic package of interbedded sandstone, siltstone and mudstone. |
| Definition of Lower Boundary: |
In 110/2b-10, the base of the Tormentil Volcanics is taken at the abrupt downward change from basalt to secondarily reddened mudstone of the Kidston Group (youngest dated interval is Langsettian). Elsewhere in the basin, the unit is likely to rest on lithologically varied Silesian sediments. The zone of secondarily reddened Carboniferous may be thinner than normal beneath the Tormentil Volcanics, as in 110/2b-10.
On the wireline log of 110/2b-10, the base of the unit is marked by the abrupt and large downward increase in gamma values, and a small downward decrease on the sonic log. The 13-20 API gamma values displayed by the basalt are similar to those of thick Carboniferous sandstones (e.g. 110/20-1), and conceivably, where basalt rests directly on sandstone, there may be little gamma shift at the base of the unit. There is apparently little downward change in average density values across the boundary. |
| Definition of Upper Boundary: |
In 110/2b-10, the top of the putative volcaniclastic sediments is marked by the sharp downward change from aeolian sandstone of the Collyhurst Sandstone Formation to (?volcaniclastic) mudstone. The top of the lavas is marked by the sharp downward change from siltstone to basalt.
On the wireline logs of 110/2b-10, there is a very sharp downward increase in gamma values and coincident sharp downward increase in velocity and density from aeolian sandstone to ?volcaniclastic mudstone. The contact of the ?volcaniclastic sediment on basalt is marked by the abrupt downward decrease in gamma values, and an additional downward increase in velocity and density. |
| Thickness: |
In 110/2b-10, the basalts are 45.5 m thick, and the overlying putative volcaniclastic sediments are 22 m thick. |
| Geographical Limits: |
The Tormentil Volcanics has been firmly identified only in 110/2b-10; its possible presence in 110/2b-9 is based solely on a similarity in wireline log patterns. It has not been confirmed by sampling or identification in the latter well and its occurrence must be treated with caution, until further data are available. |
| Parent Unit: |
Appleby Group (APY)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
Key section: Irish Sea well 110/02b- 10: 2098 or ?2121.5-2167 m (6883 or 76960-7110 ft) below KB (Jackson and Johnson, 1996). |
| Reference(s): |
| Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian of the Central and Northern North Sea. In Lithostratigraphic nomenclature of the UK North Sea. Knox, R W O'B, and Cordey, W G (editors). (Nottingham: British Geological Survey.) |
| Dixon, J E, Fitton, J G, and Frost, R T C. 1981. The tectonic significance of post-Carboniferous igneous activity in the North Sea Basin. 121-140 in Petroleum geology of the continental shelf of Northwest Europe. Illing, L V, and Hobson, G D (editors). (London: Heyden and Son.) |
| Trotter, P M. 1953. Reddened beds of Carboniferous age in north-west England and their origin. Proceedings of the Yorkshire Geological Society 29, 1-20. |
| Hardman, M. 1992. The East Irish Sea Basin. ?Direct evidence for Permo-Carboniferous rifting. In: Abstracts with Programme. Conference on Permo-Triassic rifting, at the Geological Society of London, October 1992. |
| Smith, D B. 1972. The British Isles. 1-33 in Falke, H (editor) Rotliegend: essays on European Lower Permian. Brill, Leiden. |
| Jackson, D I and Johnson, H, 1996. Lithostratigraphic nomenclature of the Triassic, Permian and Carboniferous of the UK offshore East Irish Sea Basin, British Geological Survey, Nottingham. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
