Delamerian Orogeny and potential foreland sedimentation: a review of age and stratigraphic constraints

A review of available geochronology and biostratigraphy leads to the conclusion that a considerable thickness of Cambrian sedimentary rocks exposed in the Arrowie and Stansbury Basins, South Australia. was probably deposited in a foreland setting during early phases of the Delamerian Orogeny. In contrast to most previous stratigraphic correlation schemes, we consider that the pre-tectonic Kanmantoo Group was deposited synchronously with the locally thick upper Hawker Group in essentially 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 convergent deformation and associated uplift within the Delamerian Orogen at about 522 Ma. This early ('Kangarooian') phase of the Delamerian Orogeny is interpreted as the progressive development of a coherent sigmoidal fold-thrust belt within the combined Fleurieu-Nackara Arcs, with locally developed high-temperature-low-pressure metamorphism and granitoid intrusions doting from about 516 Ma. The 'redbed package' is absent from the Fleurieu-Nackara Are region and displays isopach, palaeocurrent and facies trends consistent with derivation from this uplifted area or from the associated flexural bulge to the west. From seismic evidence we conclude that thick foreland basin deposits are present beneath Gulf St Vincent, Late phases of the Delamerian Orogeny led to local and relatively mild deformation of the early foreland deposits.