Changes in continental weathering and the marine redox state in the wake of the GOE: insights from the lower Pretoria Group (Transvaal Basin, South Africa)

The sedimentary rocks of the lower Pretoria Group record the first appearance of oxygen in Earth’s atmosphere and surface environments during the ca. 2.32 Ga Great Oxidation Event (GOE). While the change of ocean water redox-conditions during the GOE has been extensively investigated, the link between fluctuations in continental weathering patterns and their impact on the marine realm during this critical time interval in Earth’s history is less known. The black shales of the 2.32–2.25 Ga Timeball Hill Formation (TBH), deposited directly after the onset of atmospheric oxidation during the GOE, denoted by the disappearance of mass-independent fractionation of S-isotopes in the underlying Rooihoogte Formation, bear the potential to provide a better understanding of these processes.

Here, we report newly obtained major and trace element data of the EBA-1 drill core, covering the Rooihoogte, the Timeball Hill (including the Rietfonteindam Diamictite) and the Boshoek formations, at very high-spatial resolution, providing detailed insights into the continental weathering conditions and associated changes in the marine environment. While the Rooihoogte and lower TBH formations display intense weathering on the continents under warm climates, the weathering intensity massively decreased through the upper TBH, suggesting strong atmospheric cooling, terminating in the deposition of the Rietfonteindam Diamictite, which corresponds to a major glaciation. The overlying Boshoek Formation records a renewed increase in weathering intensity due to climatic warming. These fluctuations in weathering conditions were accompanied by changes in nutrient fluxes, which in turn influenced the oceanic redox conditions on a basin-wide if not global scale.