Contractional structures and deformational events in the Bowen, Gunnedah and Surat Basins, eastern Australia

Abstract

During the Permian and Triassic, eastern Australia was part of an active Gondwanaland convergent plate margin. The Bowen and Gunnedah Basins formed in a backarc setting, which was initially extensional, but switched to contractional in the mid-Permian, leading to the development of a major west-directed retroforeland thrust belt in the New England Orogen, and the formation of a major foreland basin phase to the west in the Bowen and Gunnedah Basins. The contractional deformational style is asymmetric, changing from the eastern side of the basins, adjacent to the thrust belt, to the western side of the basins which was not physically affected by the retrothrust belt. In the east, new thrusts are hard-linked to the growing thrust wedge further to the east, which propagated westwards and cannibalised the eastern part of the basin system. In the western part of the basin, however, the transmission of far-field compressional stresses led to the inversion of Early Permian extensional faults as thrusts, along with the development of new thrusts and backthrusts, which are not hard-linked to the retrothrust belt in the east. During the sustained period of rapid subsidence and sedimentation driven by thrust loading in the Bowen and Gunnedah Basins in the Late Permian to Late Triassic, there are several short periods of non-deposition and contraction. The contractional events were usually short-lived, less than a few million years each in duration, in an overall period of subsidence that lasted for ∼30–35 Ma. It is suggested that shallow to flat subduction over much of this period produced strong coupling across the plate boundary, which allowed the transmission of compressive far-field stresses well into the distal part of the foreland, possibly during times of global plate boundary reorganisation. A final contractional event in the early Late Cretaceous corresponds with the cessation of sedimentation in the Surat Basin, uplift and reactivation of earlier structures.