Tectonostratigraphic evolution of the Bowen–Gunnedah–Sydney Basin System in eastern Australia

The Bowen–Gunnedah–Sydney Basin System (BGSBS) of eastern Australia is over 1500 km long, a meridional, elongate basin preserving an extensive record of Permian–Triassic tectono-sedimentary evolution. This study presents the first basin-wide synthesis of its evolutionary phases: early rift 1, early rift 2, late rift, thermal subsidence and foreland loading. Early rift 1 records the onset of crustal extension, marked by half-graben formation, widespread syn-rift volcanism and predominantly subaerial fluvial–lacustrine deposition with minor marine influence. Early rift 2 reflects continued extension with reduced volcanism, showing basin-specific variability: greater marine influence in the Sydney Basin, thick coal-prone sequences in the Bowen Basin and mixed fluvial–lacustrine deposition in the Gunnedah Basin. During the late rift, rift topography was infilled with variable marine influence, prominent in the Bowen and southern Sydney basins but largely absent in the Gunnedah Basin, which remained dominantly fluvial and coal-forming. The northern Sydney Basin also developed coal during this time. The thermal subsidence phase is characterised by post-rift cooling and lithospheric subsidence, enabling widespread marine transgression, reduced subsidence rates and cessation of volcanism. Shallow-marine and deltaic systems expanded laterally across the basins. The foreland loading phase records basin-wide marine transgressions followed by deltaic-to-fluvial progradation and extensive coal accumulation, with variable marine influence. A key contribution of this study is the basin-wide correlation of the mid-Aldebaran unconformity, previously known from the Denison Trough, across the entire BGSBS, using radiogenic isotopic age data, outcrop and core analysis, and literature synthesis. Its inter-regional extent implies control by an allogenic driver, likely a compressional tectonic pulse. Additionally, five major marine incursions are traced basin-wide throughout the foreland loading phase and are interpreted as likely responses to pulses of thrust propagation associated with the Hunter-Bowen Orogeny.