Was the Great Oxidation Event a sharp or an oscillating build-up of free atmospheric oxygen? A combined S-Mo-Se isotope study of continuous drill core records through the Duitschland/ Rooihoogte and Timeball Hill Formations, Transvaal Basin, South Africa

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The first permanent rise in atmospheric oxygen levels occurred during the Paleoproterozoic Great Oxidation Event (GOE) during which oxygen concentrations rose from less than ca. 0.001% to ~1.5 % of the present atmospheric level, which paved the way for the development of all higher life forms. The disappearance of mass-independently fractionated sulfur isotopes (MIF-S) defines the GOE, but the correlation of various sedimentary successions from different parts of the Transvaal Basin make an exact timing of the GOE difficult. The current existence of two contrasting models about the onset and the timing of the GOE further complicate defining a precise timing. The first model places the onset of the GOE at 2.33 Ga that is characterized by a sharp and rapid increase in oxygen levels, whereas the second model places the onset of the GOE more than 100 million years earlier and identifies the GOE as an oscillating oxygenation event. It is therefore extremely crucial to study a continuous succession of sediments. New drill cores intersecting the entire Duitschland Formation and the overlying Lower Timeball Hill Formation allow for the first to investigate this key oxygenation event. The major goal of this project is to perform combined multiple S, Mo and Se isotope analyses on the new drill core material, which will lead to a more comprehensive understanding about the onset, the timing and the oxygen dynamics during the GOE. The combination of multiple S, Mo and Se isotopes further allows investigating the oxygenation of the oceans at that time. Of particular interest is to identify whether the mobilization of redox-sensitive elements are the result of oxidative continental weathering due to increasing atmospheric oxygen levels or result from the accumulation of oxygen in shallow-marine oxygen oases.