The dynamic influence of microbial mats on sediments: fluid escape and pseudofossil formation in the Ediacaran Longmyndian Supergroup, UK

Menon, Latha R. and McIlroy, Duncan and Liu, Alexander G. and Brasier, Martin D. (2015) The dynamic influence of microbial mats on sediments: fluid escape and pseudofossil formation in the Ediacaran Longmyndian Supergroup, UK. Journal of the Geological Society, 173 (1). pp. 177-185. ISSN 0016-7649, ESSN: 2041-479X DOI 10.1144/jgs2015-036

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Official URL: http://doi.org/10.1144/jgs2015-036

Abstract

Microbial mats are thought to have been widespread in marine settings before the advent of bioturbation, and the range of their influence on sediments is gradually becoming recognized. We propose that mat sealing can dynamically affect porewater conditions, and allow the build-up of overpressure that can drive dewatering and degassing to produce a suite of atypical fluid-escape features. Finely bedded silty and sandy laminae from the c. 560 Ma Burway Formation of the Longmyndian Supergroup, Shropshire, England, reveal evidence for sediment injection, including disrupted bedding, clastic injections, sill-like features and sediment volcanoes at sub-millimetre scale. These features are associated with crinkly laminae diagnostic of microbial matgrounds. Matground-associated sediment injection can explain the formation of several types of enigmatic discoidal impressions, common in rocks of this age, which have previously been attributed to the Ediacaran macrobiota. Serial grinding of Longmyndian forms previously described as Medusinites aff. asteroides and Beltanelliformis demonstrates that such discoidal features can be fully explained by fluid escape and associated load structures. Our observations emphasize the non-actualistic nature of shallow-marine Ediacaran sediments. Matground-associated sediment injection features provide a new insight into the interpretation of Proterozoic rocks and the biogenicity of their enigmatic discoidal markings.

Item Type: Article
Uncontrolled Keywords: NILAREP
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Journal of the Geological Society
Volume: 173
Page Range: pp. 177-185
Identification Number: 10.1144/jgs2015-036
Depositing User: Sarah Humbert
Date Deposited: 25 Apr 2017 22:07
Last Modified: 25 Apr 2017 22:07
URI: http://eprints.esc.cam.ac.uk/id/eprint/3960

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