Extensional Fault Architectures and the 4-D Evolution of the Exmouth Plateau and Exmouth Sub-Basin, NW Shelf, Australia

Abstract

The Exmouth sub-basin and the Exmouth Plateau are characterised by major NNE and N-S to NNW striking extensional fault systems that define the major sub-basins of the northern Carnarvon basin as well as the more distributed extension in the Exmouth plateau itself. Detailed interpretation of 2D regional seismic lines together with analyses of a number of modern 3D seismic volumes carried out by researchers at Royal Holloway have been combined to develop an integrated 4D evolutionary model for the tectonic evolution of the Northern Carnarvon basin and the Exmouth plateau. The oldest sections imaged in the Northern Carnarvon basin and the Exmouth Plateau is the Triassic Mungaroo delta system. Imaging of the Mungaroo underneath the Exmouth sub-basin is generally poor but in the Exmouth Plateau the Mungaroo exhibits large down to the west listric delta growth faults in the deeper Triassic strata. The dominant rift strata in the Exmouth sub-basin are Late Triassic to Mid-Jurassic growth sequences indicating the dominant phase of extension that formed the sub-basins along the inner margin of this part of the North West Shelf. In contrast the Late Triassic – Jurassic faults shown in the regional 2D seismic sections as well as in the many 3D seismic volumes across the Exmouth Plateau indicate only minor extension - generally only a few % and less than 10% stretching. Only the outermost edge of the Exmouth plateau shows major extensional faults in the transition zone to the oceanic crust of the ~136 Ma old Gascoyne abyssal plain. Very little syn-extensional sedimentation was deposited in the elongate graben systems of the Exmouth Plateau. Integration of seismic analyses, section construction and scaled analogue modelling of oblique rift systems has enable the development of an integrated 4D model for the tectono-stratigraphic evolution of this part of the North West Shelf. The implications of this model for petroleum exploration are also assessed in this paper.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015