The fragmentation of the Gondwana supercontinent during the Mesozoic Era produced tectonic features and depositional environments favorable for the genesis and entrapment of petroleum. Large-scale rifting is directly responsible for the pericratonic basins which may occur as taphrogenes or sphenochasms depending on rift phase and geometry. Deltaic environments developed

End_Page 352------------------------------

subsequently from the altered river courses as the individual continents changed shape and new embayments and seaways were opened.

During the Jurassic and Cretaceous Periods, Gondwanaland progressively fragmented into the several larger southern continents plus the numerous smaller segments which were dispersed over almost half the globe. Each pulse of separation produced sedimentary basins.

The present oceans of the Southern Hemisphere were first opened as rift systems which received essentially nonmarine sediments deposited in a tectonically active trough. As the rifts widened during Cretaceous time, the sediments became more marine. Lithology, organic content, and petroleum potential were determined by the nature of the source material, water depth, and paleolatitude. Separation of the continents continued throughout the Cenozoic and current observations suggest that the rifting process and ocean widening are still active.

Oil reserves in excess of 25 billion bbl and gas reserves of several trillion cubic feet may be attributed to the fragmentation of Gondwanaland. Typical producing provinces include the Reconcavo, Gabon, and Gippsland Shelf basins as well as the Niger and Nile deltas. Most of the petroleum reserves have been developed during the past decade.

End_of_Article - Last_Page 353------------