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The Lower Silurian Osmundsberg K-bentonite. Part I: stratigraphic position, distribution, and palaeogeographic significance

Published online by Cambridge University Press:  01 January 1998

STIG M. BERGSTRÖM
Affiliation:
Department of Geological Sciences, The Ohio State University, 155 S. Oval Mall, Columbus, Ohio 43210, USA
WARREN D. HUFF
Affiliation:
Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA
DENNIS R. KOLATA
Affiliation:
Illinois State Geological Survey, 615 E. Peabody Drive, Champaign, Illinois 61820, USA

Abstract

A large number of Lower Silurian (Llandovery) K-bentonite beds have been recorded from northwestern Europe, particularly in Baltoscandia and the British Isles, but previous attempts to trace single beds regionally have yielded inconclusive results. The present study suggests that based on its unusual thickness, stratigraphic position and trace element geochemistry, one Telychian ash bed, the Osmundsberg K-bentonite, can be recognized at many localities in Estonia, Sweden and Norway and probably also in Scotland and Northern Ireland. This bed, which is up to 115 cm thick, is in the lower–middle turriculatus Zone. The stratigraphic position, thickness variation and geographic distribution of the Osmundsberg K-bentonite are illustrated by means of 12 selected Llandovery successions in Sweden, Estonia, Norway, Denmark, Scotland and Northern Ireland. In Baltoscandia, the Osmundsberg K-bentonite shows a trend of general thickness increase in a western direction suggesting that its source area was located in the northern Iapetus region between Baltica and Laurentia. Because large-magnitude ash falls like the one that produced the Osmundsberg K-bentonite last at most a few weeks, such an ash bed may be used as a unique time-plane for a variety of regional geological and palaeontological studies.

Type
Research Article
Copyright
© 1998 Cambridge University Press

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