Depositional age of the early Paleoproterozoic Klipputs Member, Nelani Formation (Ghaap Group, Transvaal Supergroup, South Africa) and implications for low-level Re–Os geochronology and Paleoproterozoic global correlations

• We obtained new Re–Os isotope data for the Klipputs Member, Ghaap Group, S. Africa.
• The Re–Os depositional age of the Klipputs Member shales is 2479 ± 22 Ma (2σ).
• Low-level Re–Os geochronology of shales is possible with the CrVI-H2SO4 method.
• Upper Hamersley Group of W. Australia is younger than the Ghaap Group.
• The Doradale diamictite does not correlate with oldest Paleoproterozoic glacials.

We present new Re–Os isotope data from the early Paleoproterozoic Klipputs Member (Nelani Formation, Ghaap Group, Transvaal Supergroup, South Africa) to further evaluate low-level Re–Os geochronology of organic-rich sedimentary rocks and improve global correlations of Paleoproterozoic sedimentary rocks. The Klipputs Member contains Re (0.3–0.8 ppb), total Os (34–177 ppt) and common Os (192Os; 10–66 ppt) abundances that overlap upper crustal abundances of 0.2–2 ppb, 30–50 ppt, and 12–21 ppt, respectively. Five samples yield a Model 1 Re–Os date of 2479 ± 20 Ma (±22 Ma if the 187Re decay constant uncertainty is included, 2σ, Mean Square of Weighted Deviates [MSWD] = 0.01) using the CrVI-H2SO4 digestion protocol. Dissolution of the same sample powders using inverse aqua regia yields a Model 3 Re–Os date of 2862 ± 190 Ma (2σ, MSWD = 148). Comparison of Re–Os isotope data between the two methods reveals that inverse aqua regia liberated a component of radiogenic detrital Os whereas the CrVI-H2SO4 medium did not. The Re–Os date of 2479 ± 22 Ma for the Klipputs Member is consistent with published geochronological ages from underlying and overlying stratigraphic units, suggesting the CrVI-H2SO4 protocol yields accurate Re–Os depositional ages from ORS containing very low levels of hydrogenous Re and hydrogenous + radiogenic Os. Hence, there is potential for widespread application of low-level Re–Os ORS geochronology, including sedimentary successions deposited before the Great Oxidation Event. The initial 187Os/188Os (0.12 ± 0.01) from the Klipputs Member CrVI-H2SO4 regression indicates that dissolved Os in the contemporaneous local seawater originated from hydrothermal alteration of unradiogenic oceanic crust and/or cosmic dust rather than oxidative weathering of the radiogenic upper crust. In light of the Re–Os depositional age for the Klipputs Member, we propose that the stratigraphic units in the upper Hamersley Group above the Brockman Iron Formation (Western Australia) are younger than the Ghaap Group. Diamictite from the Doradale Formation in the Ghaap Group is constrained to be older than 2479 ± 22 Ma and thus may not be correlative with glacial deposits assigned to the oldest Paleoproterozoic glaciation.