ABSTRACT

A paleogeographic study of the Beagle Sub-basin of the northern Carnarvon Basin shows three major periods of paleogeographic development overprinting four separate tectonic zones. The periods are characterized by (1) initial back-rift depression sedimentation, (2) a period of active pre-breakup tectonism resulting in block faulting, trough development, and wrenching, and (3) a post-breakup period of thermal sag and marine transgression. The tectonic zones are basin-margin features, major trough depocenters, intra-basin horsts and grabens, and outer-basin platform areas. When petroleum geochemical data are superimposed upon the paleogeography, it is possible to make predictions about 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 of Jurassic age particularly likely to provide high-quality, extensive reservoir sands.