Assessing the mode and fluctuations of Earth’s surface redox changes across and after the Great Oxidation Event using a unique set of Hamersley Basin iron formations, W-Australia
Final Report Abstract
The study focuses on the geological and lithostratigraphic characteristics of two iron formation-bearing sections, originally believed to belong to different time periods—the Kungarra Formation (c. 2.4 Ga) and the Duck Creek Dolomite (DCD) (c. 1.85 Ga). However, in 2021, the Geological Survey of Western Australia (GSWA) reinterpreted the Kungarra Formation as a faulted slice of the DCD, supported by a U-Pb zircon age of 1873 ± 9 Ma from the Turee Creek Group. This reinterpretation, although not peer-reviewed, challenges over 40 years of previous studies and data, complicating the research project aimed at studying these formations as indicators of atmospheric and marine oxygen evolution. The project faced significant challenges due to this reinterpretation, limited sampling opportunities due to the Covid-pandemic, and strong detrital contamination in the sediments. This detrital overprint obscured initial seawater signals, complicating the use of trace elements and stable isotopes like Mo and Fe to study redox conditions. Despite these issues, differences between the two formations were still evident, particularly in the presence of cerium (Ce) anomalies, which suggest distinct depositional environments. The DCD samples show positive Ce anomalies, consistent with post-GOE iron formations, while the Kungarra samples lack such anomalies, supporting their original older age and suggesting lower oxygen levels at the time of deposition. Further isotope analysis (Rb-Sr) attempted to date the formations but faced difficulties due to potential post-depositional resetting. The data could either support the GSWA’s reinterpretation or suggest a syn-depositional event that altered the isotopic signatures. The study also examined the Boolgeeda Iron Formation, part of the Hamersley Group, which records a transition across the Great Oxidation Event. This section revealed two intervals of mass-dependent sulfur fractionation (MDF-S), indicating changes in atmospheric oxygen levels. The first interval (MDF-S 1) showed signs of increased oxygen and a rise in bioproductivity due to nutrient influx from continental weathering, followed by a decline in oxygen levels. The second interval (MDF-S 2) lacked these signatures, suggesting it was influenced by recycled sulfur rather than reflecting genuine changes in oxygen levels. Overall, the research highlights the complexities of interpreting ancient geochemical signals, the challenges posed by geological re-interpretations, and the intricate interactions between atmospheric, marine, and continental systems during significant events like the Great Oxidation Event.
Publications
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Selectively targeting authigenic and detrital components in impure chemical sedimentary rocks of the 1.85 Ga Duck Creek Dolomite, Western Australia. Goldschmidt2023 abstracts. European Association of Geochemistry.
Gogouvitis, Markus; Rosca, Carolina; Kleinhanns, Ilka; Havsteen, Julius; Van Kranendonk, Martin & Schoenberg, Ronny
