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Field and biostratigraphic evidence for an unconformity at the base of the Eycott Volcanic Group in the English Lake District

Published online by Cambridge University Press:  01 May 2009

David Millward  and
Stewart G. Molyneux
David Millward
Affiliation:
British Geological Survey, Windsor Court, Windsor Terrace, Newcastle upon Tyne NE2 4HB, U.K.
Stewart G. Molyneux
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
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Abstract

The Eycott Volcanic Group of the Lake District Lower Palaeozoic inlier consists of basaltic and andesite and and andesite sheets and associated, mainly coarse, volcaniclastic rocks. The volcanic rocks have been regarded previously as interdigitated with, and equivalent in age to, mudrocks of the upper part of the Skiddaw Group (Tremadoc–Llanvirn). Microfloral evidence has been quoted in support of this interpretation, but has not been substantiated by re-assessment of the critical data. Furthermore, a recent examination of the base of the Eycott Volcanic Group has shown that it rests with angular unconformity on the Skiddaw Group. Skiddaw Group rocks beneath the unconformity range in age from possible late Cambrian to early Llanvirn. The lowest part of the Eycott Volcanic Group, the Over Water Formation, consists of siltstones and tuffaceous sandstones yielding a diverse microflora, and is intercalated with two andesite sheets interpreted herein as sills. Since the currently accepted Llanvirn age for the Eycott Volcanic Group cannot be confirmed, the volcanism may have been penecontemporaneous with the Llandeilo–Caradoc Borrowdale Volcanic Group episode. There are implications for a pre-volcanic tectonic deformation episode.

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 1 , January 1992 , pp. 77 - 92
Copyright
Copyright © Cambridge University Press 1992

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