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Origin of montmorillonite in the early Jurassic shales of NW Scotland

Published online by Cambridge University Press:  01 May 2009

K. Amiri-Garroussi
K. Amiri-Garroussi
Affiliation:
Department of Geology and Mineralogy, University of Oxford, Parks Road, Oxford, OX1 3PR, England
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Summary

Clay mineral analysis of shales in the early Liassic Lower Broadford Beds of the Hebrides reveals the presence of abundant quantities of montmorillonite whereas the Upper Broadford Beds contain illite, kaolinite and subordinate mixed layer minerals together with chlorite. Montmorillonite enrichment of the Lower Broadford Beds as a consequence of recent weathering contamination by doleritic sills can effectively be ruled out. It is argued that the montmorillonite may have been derived from the weathering of basic igneous rocks exposed in the sediment source area during Late Triassic times. By Upper Broadford Beds times, the igneous source was either eroded away or transgressed by the early Liassic sea.

Type
Articles
Information
Geological Magazine , Volume 114 , Issue 4 , July 1977 , pp. 281 - 290
Copyright
Copyright © Cambridge University Press 1977

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