Pleistocene Evolution of the Bonaparte Basin (NW Australia): Basin Tectonics and Tide-Dominated Sediment Dispersal — A Modern Analogue for Ancient “Giant” Carbonate/Mixed Platform-Basin Systems?

From the Neogene to the present-day, the Bonaparte Basin (NW Shelf of Australia) formed a shallow-water continental shelf extending for more than 630 km from the coastline to the shelf-edge. Sedimentation on this very wide, mixed carbonate/clastic platform is examined using new combination of 3D and 2D seismic datasets, wireline and shallow core data.

Active deformation from the Neogene onwards reactivated Palaeozoic to Mesozoic-inherited grabens and structural highs. These mechanisms played a major role in the shaping of the continental shelf and primarily controlled the sedimentary pathways and dispersal in the Bonaparte Basin during the Quaternary. In particular, late reactivation of a paleo-graben led to the formation of 200m-deep intra-shelf basin where carbonate sediments have accumulated since the onset of the Pleistocene. The intra-shelf basin formed a > 10,000 km2 epeiric sea in the middle of the platform during periods of sea-level lowstands. Its presence directly controlled the mechanisms of “source-to-sink” sediment dispersal, as the rivers drained into the epeiric sea and never reached the shelf-edge during periods of sea-level fall and lowstand. Instead, a dense drainage network, thought to be tide-dominated, drains the epeiric sea and delivers clastic and mixed sediments to the shelf-margin and slope areas. The migration of the main valley directly controlled the local alternation of clastic-to-carbonate platform-basin sequences (3rd order) during the Pleistocene. Global sea-level changes, local subsidence rates and input of clastic sediments typically controlled the evolution of carbonate sedimentation in the intra-shelf basin and shelf-margin but basin-scale tectonics shaped a platform geometry that resulted in a tide-dominated sediment dispersal.

Giant continental shelves (up to 3000 km in width) are commonly found throughout earth history and were developed prolifically during the Palaeozoic and Mesozoic. Many similarities can be observed between some of these ancient “giants” and the recent Bonaparte Basin. A comparison of the Bonaparte Basin with the Cretaceous epeiric carbonate platform systems of Arabia underlines the potential of the former as a prime modern natural laboratory to improve understanding of the architecture and controls on carbonate and mixed giant continental shelves and a rare modern analogue to similar settings in Earth’s history.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California