The evolution of the North West Shelf

While there is probably no such things as a “typical” passive continental margin, the evolution of the North West Shelf of Australia is particularly complex. It has experienced a series of Palaeozoic and Mesozoic rift events, many of which are associated with the separation of micro-continental fragments, although the mechanism by which this occurs is unclear.

Understanding the Palaeozoic history of the margin is particularly difficult as stratigraphic successions of this age are deeply buried and, apart from on the basin margins, are not often penetrated by wells. However, the widespread availability of high quality seismic reflection data does provide some constraints. The importance of Permian rifting in controlling the fundamental architecture of the margin has become increasingly apparent, as has the complexity of events during the Triassic. Our understanding of the tectonic setting of the margin during this period of time continues to evolve.

Extensional fault activity during the Mesozoic is also more complex than previously recognised. Fault activity is clearly diachronous and the dominant fault orientation does not necessarily appear consistent with plate tectonic reconstructions, suggesting that processes other than plate boundary conditions may drive deformation. Sedimentary systems do however respond to changes in plate tectonic configuration and the evolution of the rift system.

Deformation of the margin continues after final break up (separation of Greater India and Australia), and it turns out that the margin is not particularly “passive” after all. Although not necessarily typical, the data-rich nature of the margin does provide insights into the range of processes that operate on rifted continental margins.