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Shallow-marine methane seeps, described here for the first time from the Australian Upper Paleozoic, are among few reported globally from the Carboniferous–Permian. Carbonate-cement fabrics, δ¹³C values and biota indicate that concentrations of nodules scattered in a narrow stratigraphic interval within the lower Holmwood Shale in the Irwin Basin formed in methane seeps. Based on ammonoids, this zone belongs within the Sakmarian. The Holmwood Shale overlies the glaciogenic Nangetty Formation that sits on crystalline Precambrian basement. The Holmwood is little deformed, shows low thermal maturation and has been covered by less than 1000 m of Permian and Neogene strata. The nodules are cementstone with complex multiphase cement fabric and δ¹³C values (mostly, ‐25 – -45‰ VPDB) below the ranges for normal-marine limestone and carbonate nodules common in marine shale elsewhere …