Abstract: Jurassic through Holocene Paleogeographic Evolution of the South Atlantic Ocean

David B. Walsh

Ten paleogeographic reconstructions are presented illustrating the Mesozoic fragmentation of western Gondwana and the evolution of the South Atlantic Ocean basin. The maps represent an integrated approach that combines a regional plate tectonic model with detailed lithologic data. Linear magnetic anomalies, hotspot tracks, and paleomagnetic analyses were used to constrain the paleo-plate positions of the continental blocks. Once reconstructed plate positions were established, well and outcrop data and tectonic features, such as rifts and zones of strike-slip were plotted. These reconstructed lithofacies maps were the basis for paleogeographic maps that illustrate the changing configuration of mountains, land, shallow seas, and deep ocean basins.

During Middle Jurassic through Early Cretaceous times, tensional stress in western Gondwana caused intracratonic rift basins to develop. These basins formed along the inherited structural grain of the Proterozoic Pan-African event. Thick sequences of continental fluvial and organic rich lacustrine sediments, which are analagous to present-day sediments in the East African rift, were deposited in the intracratonic rift basins. With continued oceanic spreading, sea-water sporadically invaded the 1900 km long rift system from the south across the Walvis Ridge/Rio Grande Rise and resulted in a thick Aptian age evaporite sequence. By Albian times, the south-to-north propagating rift had reached the equatorial Atlantic and the formerly non-marine intracratonic basins had evolved into passiv rift margin basins. Since Albian times, eustatic variations and climatic events control the clastic and carbonate sequences and sedimentation patterns along the margins of the South Atlantic Ocean.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994