--> Thermochronological and Geochronological Constraints on the Origin and Evolution of the Cretaceous Ceduna Sub-Basin, Great Australian Bight

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Thermochronological and Geochronological Constraints on the Origin and Evolution of the Cretaceous Ceduna Sub-Basin, Great Australian Bight

Abstract

The Ceduna Sub-basin is the main depocentre of the frontier Bight Basin, which formed as a result of the late Jurassic-Cenozoic separation of Australia and Antarctica. The sedimentary fill of the Ceduna Sub-basin is dominated by two structurally distinct deltaic lobes of Cenomanian and Santonian-Maastrichtian age with a combined thickness exceeding 12 km. These lobes are collectively known as the Ceduna Delta, which is likely the largest deltaic system to have existed in the geological history of the Australian continent. Understanding the origin and evolution the Ceduna Sub-basin is of profound importance for Mesozoic palaeogeographic reconstructions of Australia. Furthermore, this region is the focus of growing exploration interest, and thus improved knowledge of its origin and evolution is essential for reducing exploration uncertainty. However, because the Ceduna sub-basin is located completely offshore in water depths up to 5 km, to date there has been little exploratory drilling in this region, with only one well drilled in water depths >300 m. With primary data from the sub-basin itself lacking, we have collected a variety of new thermochronological (e.g. apatite fission track analysis (AFTA) and vitrinite reflectance (VR)) and geochronological (e.g. zircon U-Pb and fission track) datasets from the onshore margins and hinterland, which have a bearing on the evolution of the offshore region. These datasets include: (1) Zircon U-Pb ages from several samples of drillcore from the Lower Cretaceous Loongana Formation, which underlies the onshore Eucla Basin. Age populations within these data suggest that sediment input at this time was predominantly from the north and west. (2) AFTA and VR data from outcropping and subsurface rocks in the Eyre Peninsula, to the northeast of the Ceduna sub-basin. These data point to substantial exhumation of this region during the late Cretaceous. (3) Zircon U-Pb and fission track ages from the Turonian-Maastrichtian sequence penetrated by the offshore Gnarlyknots-1 well. These ages suggest that this sequence was largely sourced from recycled Permian-Early Cretaceous cover and underlying basement rocks eroded from the proximal, northeastern basin margin. The integration of these onshore and offshore datasets provides new, valuable insights into the Cretaceous palaeogeography of the Ceduna sub-basin, the tectonic processes controlling the input of clastic sediments, and the prospectivity of this frontier region.