DELAMERIAN OROGENY AND POTENTIAL FORELAND SEDIMENTATION - A REVIEW OFAGE AND STRATIGRAPHIC CONSTRAINTS

A review of available geochronology and biostratigraphy leads to the c onclusion that a considerable thickness of Cambrian sedimentary rocks exposed in the Arrowie and Stansbury Basins, South Australia. was prob ably deposited in a foreland setting during early phases of the Delame rian Orogeny. In contrast to most previous stratigraphic correlation s chemes, we consider that the pre-tectonic Kanmantoo Group was deposite d synchronously with the locally thick upper Hawker Group in essential ly en echelon basins during a final phase of extensional sedimentation within the Adelaide 'Geosyncllne'. The base of the locally overlying 'redbed package' (base of the Billy Creek and Minlaton Formations) is interpreted as the sedimentological signature of the onset of converge nt deformation and associated uplift within the Delamerian Orogen at a bout 522 Ma. This early ('Kangarooian') phase of the Delamerian Orogen y is interpreted as the progressive development of a coherent sigmoida l fold-thrust belt within the combined Fleurieu-Nackara Arcs, with loc ally developed high-temperature-low-pressure metamorphism and granitoi d intrusions doting from about 516 Ma. The 'redbed package' is absent from the Fleurieu-Nackara Are region and displays isopach, palaeocurre nt and facies trends consistent with derivation from this uplifted are a or from the associated flexural bulge to the west. From seismic evid ence we conclude that thick foreland basin deposits are present beneat h Gulf St Vincent, Late phases of the Delamerian Orogeny led to local and relatively mild deformation of the early foreland deposits.