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Volcanically mediated plankton blooms in the Central Belt of the Southern Uplands, Scotland, during the Llandovery

Published online by Cambridge University Press:  03 November 2011

S. Rigby  and
S. J. Davies
S. Rigby
Affiliation:
Susan Rigby, Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, U.K.
S. J. Davies
Affiliation:
Sarah J. Davies, Department of Geology, University of Leicester, University Road, Leicester LEI 7RH, U.K.
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Abstract

ABSTRACT

At Thirlestane Score and at four other localities in the Southern Uplands, graptolites of the Llandovery gemmatus Zone occur in couplets of lithologies immediately above thin ‘high-U’ bentonites. Above the bentonites, abundant graptolites, especially siculae, and a straight-line survivorship trend implies high productivity coupled with environmentally mediated mortality: the population structure expected in the early part of a plankton bloom. In the overlying facies, fewer, larger individuals and a convex survivorship curve suggest reduced productivity and internally mediated mortality. This is consistent with the later stages of a bloom where resources were waning but the ecological structure of the system was better developed. It is likely that the introduction of trace-metals, Fe or Al, to the water column via volcanic ash increased primary productivity, suggesting that macronutrients were available in the Southern Uplands system, allowing a bloom to be stimulated by the addition of volcanic products. This process is observed in modern open oceanic systems and implies a temporal continuity of control on the plankton despite complete faunal turn-over since the Silurian. These interpretations are most consistent with an open ocean geotectonic setting for the region.

Keywords

bentonitesgraptolitesLower Palaeozoicpalaeoceanography
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 91 , Issue 3-4: The Southern Uplands Terrane: Tectonics and Biostratigraphy within the Caledonian Orogen , 2000 , pp. 457 - 470
Copyright
Copyright © Royal Society of Edinburgh 2000

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