Abstract: Plate Reconstructions and Paleogeography: Guide For Petroleum Systems of the South Atlantic

Fryklund, Bob - Union Texas Petroleum; O. Lopez Gamundi - Texaco; S. Koslowski - Bridas, and Carlos Urien - Urien and Associates

Exploration along the Atlantic margin south of the Walvis-Rio Grande Rise has yielded oil in only three basins - Austral, Colorado and Orange. A review of selected well data, regional seismic, gravity and recent paleogeographic reconstructions provides an explanation and suggests future areas of high potential.

Gravity data from GeoSat were combined with published data, merged and reprocessed at a common datum. These data were attached to the plate outlines of the circum Atlantic region in the Cambridge Paleomap software. A series of six near restorations were prepared between 53Ma and 165Ma.These maps combined with well data and seismic were used to evaluate the source potential and petroleum systems of the South Atlantic. Three time slices are shown to illustrate the tectonics, paleogeography and source rock potential during the pre-rift, rift and drift stages.

The 165 Ma map shows the pre-rift configuration. A broad area of Permian source rocks may exist in front of the Paleo arcs. Source rocks have been encountered in the Colorado Basin in the Estrella 1 by UTAL et al. Maturity and extent is unknown.

The 105 Ma restoration shows narrow continental margins, few transforms and large areas of oceanic terrane overlain by marine rocks. Potential syn-rift source rocks are confined to narrow areas, which are much wider on the Argentina shelf. Drilling of the syn-rift section has been sparse, and concentrated on paleo-highs. Within the Austral, Colorado and Orange River Basins, source rocks or oil have been encountered. A detailed set of diagrams outlines the potential area of syn-rift source rocks in the Colorado Basin and gives data on their type and richness.

The 55 Ma reconstruction shows the passive margin stage. The gravity shows areas of volcanic rocks, such as the Rawson Area, hot spots, and transforms. The Isostatic Map shows areas of deltaic prisms, such as the Colorado River. The zipper like opening of the Atlantic is not nearly as clear as hot spots associated with the Walvis Ridge obscure the area. Selected regional seismic in the Colorado, Salado and San Julian show potentially thick marine source rocks in the center. However, due to drilling depth and lack of structuring no wells have penetrated the section. Modeling and geochemical data suggests that the area may contain mature source rocks. A series of petroleum system diagrams were prepared summarizing the potential of the post-rift or passive margin stage.

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