| Computer Code: |
TBT |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Llanvirn Series (OE)
— Caradoc Series (O4) |
| Lithological Description: |
Dominantly thick, massive beds of well sorted, medium-grained volcaniclastic sandstone up to 1 m thick, separated by thin volcaniclastic siltstone units up to several centimetres thick and locally with ripple cross-lamination (Bell, 1997). Over much of the outcrop, the siltstone is missing, giving the appearance of a uniform featureless sandstone. Locally, there are intraclasts
of mudstone, volcaniclastic siltstone and tuff, typically a few centimetres across. Towards the top of the formation there are some interbedded thin, dark grey mudstone units, similar to those seen in the underlying Skiddaw Group.
The age has not been constrained biostratigraphically though it is presumed to be Llanvirn or early Caradoc. |
| Definition of Lower Boundary: |
The contact is nowhere seen, locally the formation is inferred to lie unconformably above steeply dipping mudstone of the Tarn Moor Mudstone Formation (Skiddaw Group). |
| Definition of Upper Boundary: |
Overlain unconformably by rocks at the base of the Borrowdale Volcanic Group. |
| Thickness: |
At least 200 m. |
| Geographical Limits: |
Restricted to the Bampton Inlier, west of Shap, Cumbria. |
| Parent Unit: |
Borrowdale Volcanic Group (BVG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Tailbert Bank, 500 m west and north-west of Tailbert Farm, Shap, Cumbria [NY 5245 1400 to NY 5300 1465]. Bell, 1997. |
| Reference(s): |
| Bell, A M. 1997. The Skiddaw Group and its contact with surrounding rocks in the Bampton Inlier, Cumbria. British Geological Survey Technical Report WA/97/9. |
| Millward, D, McCormac, M, Hughes, R A, Entwisle, D C, Butcher, A, and Raines, R G. 2003. Geology of the Appleby district – a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 30 Appleby (England and Wales). |
| Cooper, A H, Fortey, N J, Hughes, R A, Molyneux, S G, Moore, R M, Rushton, A W A, Stone, P, Allen, P M, Cooper, D C, Evans, J A, Hirons, S R, and Webb, B C. 2004. The Skiddaw Group of the English Lake District. Memoir of the British Geological Survey. |
| Millward, D, and Stone, P. 2012. Stratigraphical framework for the Ordovician and Silurian sedimentary strata of northern England and the Isle of Man. British Geological Survey Research Report, RR/12/04. 119pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E030
E039
|
