Intermittent connectivity determines the oxygenation in the Favenc and lower Wilton packages of the greater McArthur Basin, northern Australia

The oxygenation of the Earth’s surface and its role in the evolution of life on our planet remains an enigmatic debate. Estimates from conflicting studies suggest that the Proterozoic atmosphere may contain between 0.002 and 2 wt% oxygen. The stability of oxygen levels, their distribution in past atmospheres and oceans, and their drivers are also points of contention. Such questions become challenging to address because unmetamorphosed and well-dated Proterozoic sedimentary rocks that record these signatures are uncommon. To address this, we provide new carbonate geochemistry data from the Mesoproterozoic Dook Creek Formation and the Mainoru Formation in the greater McArthur Basin, northern Australia. The depositional window for these successions is constrained by U–Pb geochronology of detrital zircon and <i>in situ</i> carbonate U–Pb age mapping. Our geochemical data (Ce/Ce*) show that the <i>ca</i> 1.6–1.5 Ga units here record variable redox conditions up stratigraphy. Notably, the change in basin-water oxygen conditions appear to not have been induced by biological processes. The heterogeneity is instead interpreted to have been directly driven by the connectivity between the basin to the open ocean and improved circulation with oxic, marine shallow waters. Geochronology of the Dook Creek Formation confirms correlation between Mount Rigg Group with the Favenc Package in the greater McArthur Basin elsewhere. The Dook Creek Formation here was deposited in a shallow-marine environment connected to the open ocean while the Mainoru Formation was partially restricted and evaporative. Intermittent restriction was likely driven by the Isan Orogeny, and limited oxygenation of the basin.