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Isolated pods of subaqueous welded ash-flow tuff: a distal facies of the Capel Curig Volcanic Formation (Ordovician), North Wales

Published online by Cambridge University Press:  01 May 2009

M. F. Howells ,
S. D. G. Campbell  and
A. J. Reedman
M. F. Howells
Affiliation:
British Geological Survey, Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed, Wales, U.K.
S. D. G. Campbell
Affiliation:
British Geological Survey, Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed, Wales, U.K.
A. J. Reedman
Affiliation:
British Geological Survey, Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed, Wales, U.K.
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Abstract

Acidic welded tuffs of the Capel Curig Volcanic Formation were deposited from ash-flows that transgressed from a proximal subaerial to a distal submarine environment. Isolated pods of welded tuff enveloped by marine sediments represent a distal facies of the formation deposited beyond the limits of the continuous ash-flow tuff sheets. Various mechanisms for the separation of the tuff pods from a parent flow are discussed and it is concluded that it is most likely that the formation of the pods was due to disruption of a subaqueous ash-flow during transport rather than by downslope collapse at the front of a previously deposited ash-flow tuff sheet.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 2 , March 1985 , pp. 175 - 180
Copyright
Copyright © Cambridge University Press 1985

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