ABSTRACT: Applications of Surface Geology Models to Subsurface Interpretations in Continental Rifted Basins

Philippe Charpentier, Jean-Jacques Jarrige, Jean-Paul Richert

Field geology surveys done from 1980 to 1987 along the Gulf of Suez, Red Sea, and in the East African rift led us to (1) compare the two in-extension domains in terms of geometry, mechanism, and timing of deformation to point out the structural and sedimentary elements useful to interpret seismic and well data and (2) propose geodynamic models to perform a more efficient exploration in other rifted basins.

Field observations show that the fault pattern is controlled by the inherited fabric of the basement, which is reactivated during the rifting process. This fabric defines the location of the oblique-to-the-rift transfer zones which cut the deformed area in losangic blocks limited by antithetic normal faults parallel to the rift. Transfer zones exhibit either strike-slip faults or local compressive structures, or horst-and-graben pattern. The interference between the normal faults and the transfer zones induces the typical zigzag pattern in which petroleum traps will have specific setting.

These synsedimentary deformations have a direct influence on the reservoir facies changes. The mechanical evolution is characterized by multistage tectonic deformations in which the doming generally approved as a first rifting initiation is not necessary to explain the observed extension. Sinking of the central trough and uplift of the rift shoulders represents the last stage of the rifting process due only to thermal subsidence. This process is important in hydrocarbon generation and migration.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990