Palaeogeography and Petroleum Potential of the Beagle Sub-Basin, Carnarvon Basin, Australia

A. E. Stephenson and J. E. Blevin

Palaeogeographic reconstructions of the Beagle Sub-basin of the Carnarvon Basin show a complex matrix of three major palaeoperiods overprinting four separate tectonic zones. The palaeoperiods are: an initial period of back-rift depression sedimentation, a period of active pre-breakup tectonism resulting in block faulting, trough development and wrenching, and a post-breakup period of thermal sag and marine transgression. The tectonic zones are: basin margin features, major trough depocentres, intra-basin horsts and grabens, and outer basin platform areas. The eleven palaeogeographic reconstructions presented give only partial support to the global eustasy hypothesis, with Beagle Sub-basin data from the Anisian to Ladinian and the Rhaetian to Pliensbachian at variance with published global sea level curves. When petroleum geochemical data are superimposed upon the palaeogeographic matrix, it is possible to predict the hydrocarbon prospectivity of the rocks deposited in various spatial and temporal zones. The most important source rocks in the southern and central parts of the Sub- basin are likely to be Triassic and Lower Jurassic lacustrine, fluvial and estuarine sediments in the Beagle and Cossigny Troughs, with hydrocarbon migration into several possible trap types predicted. In the north, the virtually unexplored Outer Beagle Platform contains abundant source, reservoirs and seal, and may be highly prospective, with two separate series of beach-barrier complexes particularly likely to provide high quality, extensive reservoir sands

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California