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Book Chapter

The origin and occurrence of subaqueous sedimentary cracks

By
Sean McMahon
Sean McMahon
Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA
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Ashleigh van Smeerdijk Hood
Ashleigh van Smeerdijk Hood
Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA
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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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Published:
January 01, 2017

Abstract

The rock record attests that sediments have cracked at or below the sediment–water interface in strictly subaqueous settings throughout Earth history. In recent decades, a number of hypotheses have been advanced to explain this phenomenon, but these are widely regarded as being mutually exclusive and there is little consensus about which model is correct. In this paper, we first review the geometries, lithologies and range of facies in which subaqueous sedimentary cracks occur in the geological record, with particular attention to cracks in carbonates. We then evaluate current models for subaqueous cracking, emphasizing that different models may be correct with respect to different sets of cracks, but that cracking is generally a two-step process involving sediment stabilization prior to disruption. We also present the results of some simple new experiments designed to test the dominant models of crack formation. These results demonstrate for the first time that microbial mats can produce thin, shallow cracks at the sediment–water interface. We conclude that the presence of cracks in marine, brackish and lacustrine rocks should not be used uncritically to infer fluctuations in salinity in the depositional environment.

Supplementary material: A video showing a micro-CT scan of a hand-sample from the Monteville Formation, South Africa is available at https://doi.org/10.6084/m9.figshare.c.3580673

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

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