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Organic diagenesis in stromatolitic dolomite and chert from the late Palaeoproterozoic McLeary Formation

Gabriel, N; Papineau, D; She, Z; Leider, A; Fogel, M; (2021) Organic diagenesis in stromatolitic dolomite and chert from the late Palaeoproterozoic McLeary Formation. Precambrian Research , 354 , Article 106052. 10.1016/j.precamres.2020.106052. Green open access

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Abstract

Extensive stromatolitic carbonate platforms developed during and after the Palaeoproterozoic Great Oxidation Event (GOE), which records a significant increase of oxygen in the atmosphere and oceans. Stromatolites link biological and non-biological processes through their microscopic organo-sedimentary structures that have the potential to provide information about microbial and diagenetic processes that operate during their formation. This study aims to document the mineralogy and organic geochemistry of microscopic diagenetic structures in the exceptionally-preserved late Palaeoproterozoic stromatolitic dolomite from the McLeary Formation of the Belcher Islands, in Nunavut, Canada. This is done to test the hypothesis that chemically oscillating reactions can influence the formation of diagenetic spheroids such as rosettes, granules, concretions, and botryoids; these reactions occur over short timescales during diagenesis, i.e. before the lithification of the sediment. Decimetre-size columnar stromatolites from the McLeary Formation contain centimetre-size pyrite concretions, which themselves also contain framboids. Inside rounded, black chert concretions and coarse quartz granules, there are filamentous microfossils composed of organic matter partly replaced by pyrite. These observations are consistent with post-depositional oxidation–reduction reactions involving organic matter and sulphate. In comparison, decimetre-size tabular bioherms of millimetre-to-centimetre size stromatolite columns contain microscopic dolomitic carbonate structures including circularly-concentric rosettes, zoned dolomite rhombs, and cavity structures of rounded equidistant laminations, all of which are layered with organic matter. All these diagenetic spheroids co-occur with circularly-concentric, equidistant and laminated minerals associated with degraded organic matter or microfossils. The composition and geometry of these features are consistent with the non-biological oxidation of biological carboxylic acids during diagenetic chemically oscillating reactions. Hence, both biological and non-biological processes play a major role in the precipitation of diagenetic spheroids in McLeary stromatolites. Increased abundance of organic matter as microbial biomass, as well as oxidised halogens and sulphate, led to widespread organic decomposition in the Palaeoproterozoic McLeary Formation. Ultimately, chemically oscillating reactions after periods of oxygenation likely play a more significant role than previously thought in the formation of diagenetic spheroids inside stromatolitic dolomite.

Type: Article
Title: Organic diagenesis in stromatolitic dolomite and chert from the late Palaeoproterozoic McLeary Formation
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.precamres.2020.106052
Publisher version: https://doi.org/10.1016/j.precamres.2020.106052
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10117881
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