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Changes in Fe-redox and Fe-species across the end-Permian ‘Dead Zone’ in the Sydney Basin, Australia (252.10 ± 0.06 Ma): Evidence from X-ray absorption spectroscopy
Swedish Museum of Natural History, Department of Paleobiology.ORCID iD: 0000-0003-2987-5559
MAX IV Laboratory, Lund University, PO Box 118, SE-221 00, Lund, Sweden.ORCID iD: 0000-0002-7604-251X
Swedish Museum of Natural History, Department of Paleobiology.
Swedish Museum of Natural History, Department of Paleobiology. MAX IV Laboratory, Lund University, PO Box 118, SE-221 00, Lund, Sweden.
2023 (English)In: Evolving Earth, ISSN 2950-1172, Vol. 1, article id 100029Article in journal (Refereed) Published
Abstract [en]

The end-Permian mass extinction event is traceable across several non-marine basins in Australia. In the Sydney Basin, the lithological succession is characterized by a change from coal seams to mudstones and sandstones, recording a major environmental change following the disappearance of the Permian vegetation. A few millimeter-thick iron-rich ‘rusty’ layer occurs between the uppermost Permian coal seam and the mudstone, a layer that extends laterally across the basin and which has also been documented from coeval successions in Antarctica. This layer is overlain by the <1.5-m-thick Frazer Beach Member, whose basal 10-cm-thick microbreccia bed comprises 99% kaolinite and quartz, and is dated as 252.10 ± 0.06 Ma. The Frazer Beach Member corresponds to the so-called end-Permian ‘Dead Zone’ lacking fossil pollen and leaves. This distinctive member was deposited directly following the extinction of the Permian peat-forming forests.

Here we identify, through X-ray absorption spectroscopy, a drastic redox shift across the extinction interval with increasing amount of reduced Fe-species followed by highly oxidized Fe-species, most resembling Fe(III) complexed with organic matter. Values subsequently normalise in younger samples through the ‘Dead Zone’, attaining only slightly higher redox-levels than before the event. The organically complexed Fe-species in the event bed is consistent with the standard Suwannee River fulvic acid, an acid Fe-complex with iron bound to organic matter, whereas the samples above and below the extinction layer yield spectra predominantly resembling magnetite (Fe3O4) mineral phase. We consider that the iron redox fluctuation marking the extinction interval is related to significant environmental changes with accumulation of organic matter following the mass extinction. The highly reduced iron in the extinction layer may relate to methane release from bacterial degradation, or emissions from clathrates. The presence of fulvic acid in the distinct iron-rich extinction layer indicates that an abrupt onset of the process of degradation of plant matter, lipids and calcium hydroxide (CaOH) took place, resulting in this ‘Death layer’. This was followed by millions of years of erosive conditions before new, complex vegetation could establish.

Place, publisher, year, edition, pages
Elsevier, 2023. Vol. 1, article id 100029
Keywords [en]
Mass extinction, Permian–Triassic boundary, Pyrite, Jarosite, Iron species, XANES, Suwanee River fulvic acid
National Category
Other Earth Sciences
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-5356DOI: 10.1016/j.eve.2023.100029OAI: oai:DiVA.org:nrm-5356DiVA, id: diva2:1814342
Funder
Knut and Alice Wallenberg Foundation, KAW -2020.0145Swedish Research Council, 2019-4061
Note

We acknowledge MAX IV Laboratory for time on Beamline Balder under Proposal 20190339. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research Council under contract 2018-07152, Vinnova, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and FORMAS under contract 2019-02496.

Available from: 2023-11-24 Created: 2023-11-24 Last updated: 2025-02-07Bibliographically approved

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