Seismic attributes mapping of Late Palaeozoic glacial deposits on the Australian Northwest Shelf

Abstract

During the Permo-Carboniferous the Gondwana supercontinent experienced the most extensive Phanerozoic glacial event, as recorded by widespread glaciogenic sediments from South America to Australia. Simultaneously the northern margin of the supercontinent was affected by the onset of the Neotethys rifting. During that period, several elements such as glacial surfaces or glacially eroded valleys suggest the presence of a terrestrial ice sheet in Western Australia, and the glacial Lyons Group has been reported from various locations in the Carnarvon Basin. Such deposits are proposed to form the lower part of the sedimentary cover of the Mermaid Nose area (Dampier Sub-basin, Northern Carnarvon Basin, NW Shelf). Therefore, a classical seismic stratigraphic approach combined with recently developed seismic attributes and innovative workflows is used to define the morphology of the Late Palaeozoic sequences, despite severe limitations in the resolution of the seismic data. Six stacked units are defined within a half-graben in a syn-rift setting. They are interpreted as a series of basal moraines followed by deposits associated with deglaciation periods. A thorough analysis of the topmost unit allows one to visualise and map the glacially related sequences and to further characterise their depositional environments. Eight sequences were defined within this last glacial event, including a well developed basal moraine followed by deposits recording the progressive flooding of the Mermaid Nose coeval with the waning of the local ice tongue. In addition, the glacially related hydrocarbon-rich deposits of the Al Khlata Formation in east-central Oman provide a most interesting parallel with the Permo-Carboniferous syn-rift deposits observed on the Australian Northwest Shelf.