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Book Chapter

Intrites’ from the Ediacaran Longmyndian Supergroup, UK: a new form of microbially-induced sedimentary structure (MISS)

By
Latha R. Menon
Latha R. Menon
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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Duncan McIlroy
Duncan McIlroy
Department of Earth Sciences, Memorial University of Newfoundland, St John’s, NL, A1B 3X5, Canada
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Martin D. Brasier
Martin D. Brasier
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UKDepartment of Earth Sciences, Memorial University of Newfoundland, St John’s, NL, A1B 3X5, Canada
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Published:
January 01, 2017

Abstract

Simple discoidal impressions are the only evidence of complex life in some Ediacaran and older rocks, but their interpretation is notoriously difficult. We reassessed a puzzling discoidal form from the c. 560 Ma upper Burway Formation of the Ediacaran Longmyndian Supergroup, Shropshire, UK. The structures, previously described as Intrites punctatus Fedonkin, are found on both the bed tops and soles. They vary in morphology from mounds with central depressions to incomplete rings and pairs of short ridges. Examination of the purported Intrites documented from the Longmyndian in cross-section revealed a torus-shaped structure bounded by microbial mat layers and commonly containing white laminae. We interpret the ‘Longmyndian Intrites’ as a product of microbial trapping, sediment binding and authigenic clay mineral and carbonate precipitation on the flanks of small sediment volcanoes. Subsidence of the ring-like structure into muddy sediments resulted in a torus-shaped microstromatolite. Preferential stromatolitic growth parallel to the prevailing current produced the observed partial rings or parallel ridges and explains their preferential orientation as current alignment. This interpretation of ‘Longmyndian Intrites’ expands the known variety of microbially-induced sedimentary structures (MISS) and emphasizes the importance of considering microbially-induced structures and abiological processes when interpreting discoidal impressions in ancient rocks.

Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

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Contents

Geological Society

Earth System Evolution and Early Life: A Celebration of the Work of Martin Brasier

A. T. Brasier
A. T. Brasier
University of Aberdeen, UK
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D. McIlroy
D. McIlroy
Memorial University of Newfoundland, Canada
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N. McLoughlin
N. McLoughlin
Rhodes University, South Africa
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Geological Society of London
Volume
448
ISBN electronic:
9781786202932
Publication date:
January 01, 2017

GeoRef

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