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Assessment of Hirnantian synglacial eustacy and palaeogeography in a tectonically active setting: the Welsh Basin (UK)

Published online by Cambridge University Press:  19 July 2013

DAVID M. D. JAMES
DAVID M. D. JAMES*
Affiliation:
School of Earth and Ocean Sciences, Cardiff University, Wales, UK
*
*E-mail: [email protected]
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Abstract

The Hirnantian stratigraphy of Wales is critically assessed against the global evidence for two major Hirnantian synglacial eustatic lowstands. The evidence for two separate lowstands of relative sea level is locally suggestive in shelf sequences but generally only permissive in the basin. Nowhere can the possible candidate lowstands be separated biostratigraphically and thus basinwide correlation that might rule out local tectonic control is impossible to prove. Consistent with palaeolatitude evidence and a situation far removed from the Gondwana margin, there is no facies evidence (e.g. dropstones) for local glacial conditions and the diamictites are of mass-flow origin. Sequence stratigraphic reasoning proves helpful in the correlation of the basinal succession in Central Wales with the shelf sequences along the Tywi Lineament and the Variscan Front, and suggests that the first appearance of Normalograptus persculptus in Wales does not correspond with the base of the persculptus Biozone. Extensive new palaeocurrent data and sedimentological restudy is combined with review of earlier knowledge to argue for significant revisions to previous palaeogeographic maps for ‘generalized lowstand conditions’, notably along the Bala Lineament, the Variscan Front and the Central Wales Inliers.

Keywords

HirnantianWelsh Basinglacio-eustacypalaeogeographydiamictites
Type
Original Articles
Information
Geological Magazine , Volume 151 , Issue 3 , May 2014 , pp. 447 - 471
Copyright
Copyright © Cambridge University Press 2013 

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