The BGS Lexicon of Named Rock Units — Result Details

Skiddaw Group (Metasomatically Altered) [Obsolete Usage: Use SKG]

Computer Code: SKGM Preferred Map Code: SKG'
Status Code: Index Level
Age range: Tremadoc Series (O1) — Llanvirn Series (OE)
Lithological Description: Silty mudstone with some turbidite sandstone.
Definition of Lower Boundary: The southern boundary is gradational over a few tens of metres into unbleached dark grey mudstone of the Skiddaw Group. The northern contact occurs at a fault or unconformity and thus major change in lithology, with the Borrowdale Volcanic Group. The metasomatic alteration is associated with tourmaline veins and possibly due to a concealed intrusion (Ulverston memoir, Johnson et al 2001).
Definition of Upper Boundary: In the Black Combe inlier, the top is not seen, but t is unconformably overlain by the Borrowdale Volcanic Group or is faulted against Carboniferous rocks. In the northern part of the Skiddaw inlier, the youngest siltstones and mudstones of the Kirk Stile Formation of the Skiddaw Group, are unconformably overlain by volcanogenic mudstones and andesites of the Eycott Volcanic Group.
Thickness: In the Skiddaw inlier less than 5000 m thick, in the Black Combe inlier more than 1000 m thick.
Geographical Limits: Metasomatised Skiddaw Group rocks crop out in the Skiddaw Inlier, Cross Fell inlier and the Black Combe Inlier. The Black Combe Inlier is about 50 square kilometres in area and is bounded to the west by down-faulted Carboniferous and Permo-Triassic strata and to the north, east and south by unconformably overlying or down-faulted Borrowdale Volcanic Group rocks. The Skiddaw inlier is locally unconformably overlain by Eycott Volcanic Group rocks, elsewhere the boundaries are faulted.
Parent Unit: Not Applicable (-)
Previous Name(s): Skiddavian (Series) (-3032)
Skiddaw Slate Group (-4329)
Skiddaw Slates [Obsolete Name And Code: See SKG And SKGM] (SKSL)
Grits In Skiddaw Slates [Obsolete Name And Code: Part Of SKG Or SKGM] (GTSK)
Skiddavian [Obsolete Name And Code: See SKG And SKGM] (SKVN)
Slates And Sandstones In Skiddaw Slates [Obsolete Name And Code: part of SKG or SKGM] (SLS)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Black Combe Johnson, Soper and Burgess, 2001. 
Reference(s):
Cooper, A H and Molyneux, S G, 1990. The age and correlation of Skiddaw Group [early Ordovician] sediments in the Cross Fell Inlier [northern England]. Geological Magazine, Vol.127, 147-157. 
Fortey, N J, 1989. Low grade metamorphism in the Lower Ordovician Skiddaw Group of the Lake District, England. Proceedings of the Yorkshire Geological Society, Vol.47(4), 325-337. 
Johnson, E W, Soper, N J, Burgess, I C, Ball, D F, Beddoe-Stephens, B, Carruthers, R M, Fortey, N J, Hirons, S, Merritt, J W, Millward, D, Roberts, B, Walker, A B and Young, B. 2001. Geology of the country around Ulverston. Memoir of the British Geological Survey, England and Wales, Sheet 48. 
Cooper, A H, Rushton, A W A, Molyneux, S G, Hughes, R A, Moore, R M and Webb, B C. 1995. The stratigraphy,correlation, provenance and palaeogeography of the Skiddaw Group (Ordovician) in the English Lake District. Geological Magazine, Vol.132(2), 185-211. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E048