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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. LU and Lee, M. R. (2017) In Earth and Planetary Science Letters 460. p.192-200
Abstract

The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralisation. 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... (More)

The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralisation. 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.

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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
bacterial sulphate reduction, impact hydrothermal, rochechouart impact, sulphur stable isotopes
in
Earth and Planetary Science Letters
volume
460
pages
9 pages
publisher
Elsevier
external identifiers
  • scopus:85007508486
ISSN
0012-821X
DOI
10.1016/j.epsl.2016.12.023
language
English
LU publication?
no
id
6342bf04-1143-49fc-9f2d-08796ca526ac
date added to LUP
2017-06-16 15:41:55
date last changed
2018-01-07 12:08:21
@article{6342bf04-1143-49fc-9f2d-08796ca526ac,
  abstract     = {<p>The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralisation. 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 δ<sup>34</sup>S values vary over a wide range, from −35.8‰ to +0.4‰. The highest values, δ<sup>34</sup>S −3.7‰ to +0.4‰, are recorded in the coherent basement, and likely represent a primary terrestrial sulphur reservoir. Sulphides with the lowest values, δ<sup>34</sup>S −35.8‰ to −5.2‰, are hosted within locally brecciated and displaced parautochthonous and autochthonous impactites. Intermediate δ<sup>34</sup>S 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.</p>},
  author       = {Simpson, S. L. and Boyce, A. J. and Lambert, P. and Lindgren, P. and Lee, M. R.},
  issn         = {0012-821X},
  keyword      = {bacterial sulphate reduction,impact hydrothermal,rochechouart impact,sulphur stable isotopes},
  language     = {eng},
  month        = {02},
  pages        = {192--200},
  publisher    = {Elsevier},
  series       = {Earth and Planetary Science Letters},
  title        = {Evidence for an impact-induced biosphere from the δ<sup>34</sup>S signature of sulphides in the Rochechouart impact structure, France},
  url          = {http://dx.doi.org/10.1016/j.epsl.2016.12.023},
  volume       = {460},
  year         = {2017},
}