Abstract: Visualization of the Relationship Between Changing Paleogeography of the South Atlantic and Hydrocarbon Play Element Evolution

Norton, Ian O.; Smith, P. R.; Swanson, W. A.; Creaney, S. - Exxon Exploration Company

In any hydrocarbon system there are strong links between tectonic evolution, drainage patterns and eustacy. Interplay between these large-scale geologic factors leads to variations in critical hydrocarbon play elements. We illustrate some aspects of this interplay using an analysis of the South Atlantic. Results are presented in a series of paleogeographic maps that incorporate data from both the African and South American margins. Computer animation and morphing of the paleogeography are used to better visualize evolutionary changes. Integration of data from both sides allows use of data from one margin to complement data from the opposite side where coverage may not be as good. Initial rifting in the South Atlantic was strongly asymmetric, as was the final break to oceanic crust. This led to preservation of syn-rift source rocks in wide rift zones on one side of the Atlantic where the conjugate margin may have barely any rift section remaining (e.g., Gabon versus Sergipe Alagoas). Effective source richness increases to the south through the whole basin, which we interpret as a consequence of syn-rift drainage patterns that produced fluvial sediment in the north, thereby diluting the lacustrine source rock. Initially rapid sea floor spreading resulted in for rapid subsidence and cooling of the rift and early post-rift section, increasing chance of source preservation. Source rock preserved in this manner was finally heated to maturity during the Tertiary, when uplift of both Africa and South America resulted in deposition of large volumes of clastics and deep burial of the source rocks.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil