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Type: Journal article
Title: Microbial assemblage and palaeoenvironmental reconstruction of the 1.38 Ga Velkerri Formation, McArthur Basin, northern Australia
Author: Jarrett, A.
Cox, G.
Brocks, J.
Grosjean, E.
Boreham, C.
Edwards, D.
Citation: Geobiology, 2019; 17(4):1-21
Publisher: John Wiley & Sons
Issue Date: 2019
ISSN: 1472-4677
Statement of
Amber J. M. Jarrett, Grant M. Cox, Jochen J. Brocks, Emmanuelle Grosjean Chris J. Boreham, Dianne S. Edwards
Abstract: The ca. 1.38 billion years (Ga) old Roper Group of the McArthur Basin, northern Australia, is one of the most extensive Proterozoic hydrocarbon-bearing units. Organic-rich black siltstones from the Velkerri Formation were deposited in a deep-water sequence and were analysed to determine their organic geochemical (biomarker) signatures, which were used to interpret the microbial diversity and palaeoenvironment of the Roper Seaway. The indigenous hydrocarbon biomarker assemblages describe a water column dominated by bacteria with large-scale heterotrophic reworking of the organic matter in the water column or bottom sediment. Possible evidence for microbial reworking includes a large unresolved complex mixture (UCM), high ratios of mid-chained and terminally branched monomethyl alkanes relative to n-alkanes-features characteristic of indigenous Proterozoic bitumen. Steranes, biomarkers for single-celled and multicellular eukaryotes, were below detection limits in all extracts analysed, despite eukaryotic microfossils having been previously identified in the Roper Group, albeit largely in organically lean shallower water facies. These data suggest that eukaryotes, while present in the Roper Seaway, were ecologically restricted and contributed little to export production. The 2,3,4- and 2,3,6-trimethyl aryl isoprenoids (TMAI) were absent or in very low concentration in the Velkerri Formation. The low abundance is primary and not caused by thermal destruction. The combination of increased dibenzothiophene in the Amungee Member of the Velkerri Formation and trace metal redox geochemistry suggests that degradation of carotenoids occurred during intermittent oxygen exposure at the sediment-water interface and/or the water column was rarely euxinic in the photic zone and likely only transiently euxinic at depth. A comparison of this work with recently published biomarker and trace elemental studies from other mid-Proterozoic basins demonstrates that microbial environments, water column geochemistry and basin redox were heterogeneous.
Keywords: McArthur Basin; Proterozoic; anoxia; biomarkers; eukaryotes; euxinia; hydrocarbons; phototrophic sulphur bacteria; redox
Rights: © 2019 Commonwealth of Australia. Geobiology © 2019 John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
RMID: 0030108225
DOI: 10.1111/gbi.12331
Grant ID:
Appears in Collections:Geology & Geophysics publications

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