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

大气中氧含量的第一次永久性上升发生在古元古代大氧化事件（GOE）期间，在此期间，氧浓度从不到目前大气水平的约0.001%上升到~ 1.5%，为所有高级生命形式的发展铺平了道路。独立质量分异硫同位素（MIF-S）的消失定义了GOE，但德兰士瓦盆地不同地区不同沉积序列的对比使得GOE的精确时间难以确定。目前存在的关于GOE发生和时间的两种截然不同的模型进一步复杂化了精确时间的定义。第一个模型将GOE的开始时间定为2.33 Ga，其特征是氧水平急剧快速增加，而第二个模型将GOE的开始时间定为1亿多年前，并将GOE确定为振荡氧合事件。因此，研究沉积物的连续演替是极其重要的。新的岩心穿过整个Duitschland地层和上覆的Lower Timeball Hill地层，首次研究了这一关键的氧化事件。该项目的主要目标是对新钻芯材料进行S、Mo和Se同位素组合分析，从而更全面地了解GOE的开始、时间和氧动力学。多种S、Mo和Se同位素的结合进一步研究了当时海洋的氧合情况。特别令人感兴趣的是确定氧化还原敏感元素的动员是由于大气氧含量增加引起的大陆氧化风化的结果，还是由于浅海氧气绿洲中氧气的积累。

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.