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Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England)

Wignall, P.B. (2001) Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England). Proceedings of the Geologists' Association, 112 (4). pp. 349-360. ISSN 0016-7878

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Abstract

Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay(Devon, SW England). Proceedings of the Geologists’ Association, 112. 349–360. New exposures in Pinhay Bay (SE Devon) of the White Lias (Langport Member of the Lilstock Formation)and basal Blue Lias reveal rapidly changing palaeoenvironments during the Triassic–Jurassic(T–J) boundary interval. During deposition of the topmost White Lias a soft seafloor of micritic mudstone was lithified and bored. The resultant hardground was locally eroded, probably in a shallow marine setting, to form a spectacular intraformational conglomerate that was itself lithified. Brief subaerial emergence then followed and produced a fissured and pitted top surface to the White Lias. The regression was short lived and rapid transgression at the base of the Blue Lias established organic-rich shale deposition with a small framboidal pyrite population and low Th/U ratios indicative of a stable, sulphidic lower water column (euxinic conditions). The White Lias/Blue Lias contact thus records a short duration, high amplitude relative sea-level change. This sea-level oscillation has also been postulated for other T–J boundary sections in Europe, although the failure to identify it in regional-scale sequence stratigraphic studies is probably due to its brief duration. Deposition of the basal beds of the Blue Lias was marked by a discrete phase of syn-sedimentary folding and small growth fault activity that may record a regional pulse of extensional tectonic activity.

Item Type: Article
Copyright, Publisher and Additional Information: © 2001 Geologists’ Association. This material has been published in Proceedings of the Geologists' Association, the only definitive repository of the content that has been certified and accepted after peer review. Copyright and all rights therein are retained by the Geological Society of London.
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds)
Depositing User: Sherpa Assistant
Date Deposited: 20 May 2005
Last Modified: 05 Jun 2014 20:02
Published Version: http://www.ingentaconnect.com/content/geol/pga
Status: Published
Refereed: Yes
URI: http://eprints.whiterose.ac.uk/id/eprint/475

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