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Faunal transport within event horizons in the British Upper Silurian

Published online by Cambridge University Press:  01 May 2009

Charlie J. Underwood
Charlie J. Underwood
Affiliation:
Department of Earth Sciences, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK
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Abstract

Many marine fossil concentrations are considered the result of episodic sedimentological events, and in particular those due to storms. Most storm or tempestite concentrations are identified as autochthonous or parautochthonous assemblages created by a variety of winnowing processes within shallow water environments. In contrast, samples described here from both a ‘shelf’ and a ‘basinal’ setting within the Ludlow (Upper Silurian) succession of the Welsh Basin reveal the presence of a biota transported by tempestite activity into a setting dominated by a more offshore biota. Tempestite horizons from within an ‘outer shelf’ mud dominated setting include shelly lenses with a transported fauna abounding in gastropods, tentaculitids and atrypid brachiopods, the background sediment being rich in graptolites, cephalopods and small strophomenid brachiopods. Within the ‘basinal’ area, distal tempestites range from minor siltstone layers to thicker bioclastic limestone lenses. The siltstones are largely graptolitic (dominated by Bohemograptus), with some small brachiopods, whilst Saetograptus colonus is the only common graptolite in the limestones, which also contain a fauna of broken brachiopods and bryozoa. The transport of assemblages distally into a variety of settings represents a potential source of error in palaeoecological analysis. Transported assemblages may, however, provide evidence of the composition of both benthic and pelagic shallower water faunas no longer known in situ.

Type
Articles
Information
Geological Magazine , Volume 131 , Issue 4 , July 1994 , pp. 485 - 498
Copyright
Copyright © Cambridge University Press 1994

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