Past oceanic sulphate concentration is important for understanding how the oceans’ redox state responded to atmospheric oxygen levels. The absence of extensive marine sulphate evaporites before ∼1.2 Gyr probably reflects low seawater sulphate and/or higher carbonate concentrations. Sulphate evaporites formed locally during the 2.22–2.06 Gyr Lomagundi positive δ13C excursion. However, the ∼2.2–2.1 Gyr Lucknow Formation, South Africa, provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input. These marginal marine deposits contain evidence for evaporite molds, pseudomorphs after selenite gypsum, and solid inclusions of Ca‐sulphate in quartz. Carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines. The apparent precipitation of gypsum before halite requires ≥2.5 mm L−1 sulphate concentration, higher than current estimates for the Paleoproterozoic. During the Lomagundi event, which postdates the 2.32 Gyr initial rise in atmospheric oxygen, seawater sulphate concentration rose from Archean values of ≤200 μm L−1, but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state.

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The June Hill Volcanics occupy a central stratigraphic position in the tectonic evolution of the Capricorn Orogeny that occurred along the southwestern margin of the Pilbara Craton in Palaeoproterozoic time. The volcanic rocks have been interpreted alternatively as due to continental rifting, foreland‐basin development, or backarc extension. Previous multigrain zircon U–Pb results from these rocks, as well as from an unnamed rhyolitic porphyry that is interstratified in turbidites of the overlying Ashburton Formation, are influenced by the combined effects of Pb loss and xenocrystic inheritance. We report new SHRIMP zircon ages of 1799 ± 8 and 1786 ± 11 Ma, respectively from the June Hill Volcanics and the unnamed porphyry, both of which have been deformed during the Capricorn Orogeny. Close similarity between these ages and results from various late‐stage Capricorn granitoids (including our new SHRIMP result of 1795 ± 8 Ma for the Minnie Creek granite) imply rapid development of the western Ashburton Trough, accumulating and deforming ∼10 km of turbiditic sediments in about 10 million years. Comparison of our new June Hill age with previous SHRIMP results from the central Ashburton Trough implies that foreland‐basin development of the Capricorn Orogeny was significantly diachronous, younging westward during oblique Pilbara–Yilgarn convergence.

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