Mid-Cretaceous uplift and denudation of the Bowen and Surat Basins, eastern Australia: relationship to Tasman Sea rifting from apatite fission-track and vitrinite-reflectance data

Interpretation of apatite fission-track and vitrinite-reflectance data for samples from nine petroleum-exploration wells in the eastern part of the Bowen and Gunnedah Basins, eastern Australia, indicates that peak paleotemperatures were reached during the Early Cretaceous, through progressive exposure to higher temperatures due to increased depth of burial. The paleotemperatures were 28-58C higher than at present. Cooling from the peak temperatures took place in the mid-Cretaceous, at some time during the interval 100-80 Ma, with the greatest amount of cooling occurring in the northern part of the study area. Paleogeothermal gradients were generally in the range 21-35C/km, similar to present-day geothermal gradients in the region. The estimated maximum amount of denudation in the study area is 1.9km, with a significant portion of the eroded succession being Jurassic to Early Cretaceous in age. The synchronicity between the times of cooling inferred from all the sampled wells, regardless of their location with respect to the fault system near the present eastern margin of the Bowen Basin, suggests that the uplift was widespread, rather than being localised by faults during the mid-Cretaceous. This can be correlated with uplift along much of the eastern margin of Gondwanaland at the same time, including all of eastern Australia, in New Zealand and in Marie Byrd Land, Antarctica. The onset of this mid-Cretaceous regional cooling and denudation coincided with a period of continental extension after the cessation of volcanism and subduction at about 95 Ma, and prior to the initiation of seafloor spreading at about 84 Ma and formation of the current passive margin.