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Xenon isotopes in Archean and Proterozoic insoluble organic matter: a robust indicator of syngenecity?

Bekaert, D. V. and Broadley, M. W. and Delarue, F. and Druzhinina, Z. and Paris, G. and Robert, F. and Sugitani, K. and Marty, B. (2020) Xenon isotopes in Archean and Proterozoic insoluble organic matter: a robust indicator of syngenecity? Precambrian Research, 336 . Art. No. 105505. ISSN 0301-9268. https://resolver.caltech.edu/CaltechAUTHORS:20191023-152951528

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Abstract

Insoluble organic materials (kerogens) isolated from ancient sedimentary rocks provide unique insights into the evolution of early life. However, establishing whether these kerogens are indeed syngenetic with the deposition of associated sedimentary host rocks, or contain contribution from episodes of secondary deposition, is not straightforward. Novel geochemical criterions are therefore required to test the syngenetic origin of Archean organic materials. On one hand, the occurrence of mass-independent fractionation of sulphur isotopes (MIF-S) provides a tool to test the Archean origin of ancient sedimentary rocks. Determining the isotope composition of sulphur within kerogens whilst limiting the contribution from associated minerals (e.g., nano-pyrites) is however challenging. On the other end, the Xe isotope composition of the Archean atmosphere has been shown to present enrichments in the light isotopes relative to its modern composition, together with a mono-isotopic deficit in ¹²⁹Xe. Given that the isotopic composition of atmospheric Xe evolved through time by mass dependent fractionation (MDF) until ∼2.5-2.0 Ga, the degree of MDF of Xe isotopes trapped in kerogens could provide a time stamp for the last chemical equilibration between organic matter and the atmosphere. However, the extent to which geological processes could affect the signature of Xe trapped in ancient kerogen remains unclear. In this contribution, we present new Ar, Kr and Xe isotopic data for four kerogens isolated from 3.4 to 1.8 Gy-old cherts and confirm that Xe isotopes from the Archean atmosphere can be retained within kerogens. However, new Xe-derived model ages are lower than expected from the ages of host rocks, indicating that initially trapped Xe components were at least partially lost and/or mixed together with some Xe carried out by younger generations of organic materials, therefore complicating the Xe-based dating method. Whilst non-null Δ³³S values and ¹²⁹Xe deficits relative to modern atmosphere constitute reliable imprints from the Archean atmosphere, using Xe isotopes to provide information on the syngenetic origin of ancient organic matter appears to be a promising - but not unequivocal - tool that calls for further analytical development.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.precamres.2019.105505DOIArticle
Additional Information:© 2019 The Authors. Published by Elsevier B.V. Under an Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Received 17 August 2019, Revised 15 October 2019, Accepted 16 October 2019, Available online 18 October 2019. This study was supported by the European Research Council (grants PaleoNanoLife 2011-ADG_20110209 to F.R. and PHOTONIS 695618 to B.M.). We gratefully thank Raymond Michels and Laurette Piani for providing us with some bulk rock of the bituminous laminites of Orbagnoux, and some IOM from the meteorite GRO 95502, respectively. This is CRPG contribution n°2727. The authors declare no conflict of interest.
Funders:
Funding AgencyGrant Number
European Research Council (ERC)PaleoNanoLife 2011-ADG_20110209
European Research Council (ERC)PHOTONIS 695618
Record Number:CaltechAUTHORS:20191023-152951528
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191023-152951528
Official Citation:D.V. Bekaert, M.W. Broadley, F. Delarue, Z. Druzhinina, G. Paris, F. Robert, K. Sugitani, B. Marty, Xenon isotopes in Archean and Proterozoic insoluble organic matter: A robust indicator of syngenecity?, Precambrian Research, Volume 336, 2020, 105505, ISSN 0301-9268, https://doi.org/10.1016/j.precamres.2019.105505. (http://www.sciencedirect.com/science/article/pii/S0301926819303535)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99421
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 Oct 2019 23:01
Last Modified:04 Nov 2019 22:40

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