Evidence for an impact-induced biosphere from the δ34S signature of sulphides in the Rochechouart impact structure, France

Simpson, S.L., Boyce, A.J. , Lambert, P., Lindgren, P. and Lee, M.R. (2017) Evidence for an impact-induced biosphere from the δ34S signature of sulphides in the Rochechouart impact structure, France. Earth and Planetary Science Letters, 460, pp. 192-200. (doi:10.1016/j.epsl.2016.12.023)

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Abstract

The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralization. The sulphides can be divided into four types on the basis of their mineralogy and host rock. They range from pyrites and chalcopyrite in the underlying coherent crystalline basement to pyrites hosted in the impactites. Sulphur isotopic results show that δ34S values vary over a wide range, from -35.8‰ to +0.4‰. The highest values, δ34S -3.7‰ to +0.4‰, are recorded in the coherent basement, and likely represent a primary terrestrial sulphur reservoir. Sulphides with the lowest values, δ34S -35.8‰ to -5.2‰, are hosted within locally brecciated and displaced parautochthonous and autochthonous impactites. Intermediate δ34S values of -10.7‰ to -1.2‰ are recorded in the semi-continuous monomict lithic breccia unit, differing between carbonate-hosted sulphides and intraclastic and clastic matrix-hosted sulphides. Such variable isotope values are consistent with a biological origin, via bacterial sulphate reduction, for sulphides in the parautochthonous and autochthonous units; these minerals formed in the shallow subsurface and are probably related to the post impact hydrothermal system. The source of the sulphate is likely to have been seawater, penecontemporaneous to the impact, as inferred from the marginal marine paleogeography of the structure. In other eroded impact craters that show evidence for impact-induced hydrothermal circulation, indirect evidence for life may be sought isotopically within late-stage (≤120°C) secondary sulphides and within the shocked and brecciated basement immediately beneath the transient crater floor.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Lindgren, Dr Paula and Simpson, Ms Sarah and Boyce, Professor Adrian and Lee, Professor Martin
Authors: Simpson, S.L., Boyce, A.J., Lambert, P., Lindgren, P., and Lee, M.R.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Earth and Planetary Science Letters
Publisher:Elsevier
ISSN:0012-821X
ISSN (Online):1385-013X
Published Online:09 January 2017
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Earth and Planetary Science Letters 460:192-200
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
602461Reconstructing thermal and fluid alteration histories of planetary materials.Martin LeeScience & Technologies Facilities Council (STFC)ST/K000942/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES