The Bowen-Gunnedah-Sydney Basin System (BGSBS) of eastern Australia preserves one of the most complete, continuous (over 2000 km), and well-documented records of Permo-Triassic sedimentation in the Southern Hemisphere. Although stratigraphic thickness varies among the basins, they exhibit broadly comparable sedimentary facies and record a shared sequence of basin-forming processes, including crustal extension, thermal subsidence, and foreland loading, with minor differences in the timing and duration of each phase.

This study integrates published stratigraphic and geochronologic data with wireline log interpretations from approximately 500 drillholes to (1) evaluate spatial and temporal variations in rifting, thermal subsidence, and foreland loading across the basin system and assess stratigraphic continuity between basins, and (2) test the basin-wide correlatability of key stratigraphic surfaces, such as unconformities and marine transgressions, and their controlling mechanisms.

Basin development commenced in the Early Permian as an array of extensional depocenters characterized by volcanic deposits, followed by lacustrine, alluvial, coastal, and shallow-marine sedimentation, including coal accumulation within isolated graben and half-graben structures. This pattern characterizes all three basins, although the timing of formation of extensional depocenters varies north-south. Several, probably diachronous marine transgressions characterized this phase of basin history. An interval of passive thermal subsidence subsequently produced a basin-wide marine transgression. This led to the accumulation of largely continuous marine successions throughout the Sydney and Gunnedah basins (and possibly the Bowen Basin), although much of this phase is missing from the Bowen Basin due to uplift and erosion associated with the mid-Aldebaran Unconformity. This unconformity can be traced throughout the entire basin system and is therefore likely to be tectonically forced. The onset of foreland loading in the basin occurred earlier in the east than in the west, consistent with the direction of plate convergence during the formative Hunter-Bowen contractional event. The foreland loading phase gave rise to a single, continuous, north-south-elongate basin with cross-sectional asymmetry, the depocenter being located close to the eastern basin margin. Several marine transgressions during this phase can be traced across and between the three basins, suggesting an external forcing control. Late Permian marine strata evolved over time to a largely nonmarine Triassic fill, indicating that the retroarc foreland basin transitioned from an underfilled to an overfilled condition.