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Evidence for contemporaneous deposition of the Duitschland and Rooihoogte formations (Transvaal Supergroup): Implications for tempo and mode of Earth’s Great Oxidation

Abstract

The stratigraphic correlation of the ca. 2353 ± 18 Ma to 2316 ± 7 Ma Duitschland and Rooihoogte formations, Transvaal Supergroup, South Africa, becomes critically important when viewed in the light of the Great Oxidation Event (GOE), since both formations record the transition from mass-independent (MIF-S) to mass-dependent fractionation of sulfur isotopes (MDF-S) indicative of the transition to an oxygenated atmosphere. At present, discrepancies exist as to whether the Duitschland and Rooihoogte formations are two distinct formations, formed in an older and younger depositional basin, respectively, or alternatively were deposited contemporaneously in the same basin at different positions to shorelines of the basin. A decoupled depositional history would indicate an oscillating oxygenation trajectory of the planet, whereas a contemporaneous deposition of the two formations would point towards a sudden increase of atmospheric oxygen. To investigate the controversy of a contemporaneous versus a consecutive depositional relationship, this study presents a sedimentological investigation of 11 stratigraphic profiles intersecting the Duitschland to lower Timeball Hill and Rooihoogte to lower Timeball Hill formations. The 11 profiles are correlated between the Transvaal Supergroup in the Transvaal area of South Africa and the adjoining Kanye area in Botswana and show that the Duitschland and Rooihoogte formations are laterally correlative. The sedimentological observations are reinforced by similar major and trace element data as well as Sr–Nd isotope compositions measured in four scientific drill cores, intersecting both the Duitschland and the Rooihoogte formations. Consequently, the documented disappearance of MIF-S in these two formations should be regarded as a single-step atmospheric change, thereby removing the best supporting evidence for a protracted and dynamic oxygenation trajectory. Furthermore, bulk sediment T DM(Nd) of the Duitschland and Rooihoogte formations consistently display Archean crustal residence ages in the interval between 2.9 Ga and 3.3 Ga for most samples. Geochemical discrimination functions and zircon distribution patterns suggest a collisional tectonic setting and measured bulk sediment Nd isotope data combined with literature zircon Hf isotope data indicate a potential collision between a Rae-type craton and the Kaapvaal craton around 2.5 Ga.</p

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