AL-RAISI, MUATASM, and CHRISTOPHER G. ST. C. KENDALL
University of South Carolina, Columbia SC 29208

Abstract: Stuctural and Depositional Controls on the Sedimentary Fill of the Algoa Basin, South Africa, and its Hydrocarbon Potential

The Algoa Basin, located on the southeastern margin of South Africa, is a rift basin that covers an offshore area of some 4000 square kilometers. A detailed seismic stratigraphic interpretation of the Aptian to Albian Drift Sequence of this basin, is coupled to a determination of the hydrocarbon potential of the deep water systems in the basin. The study involves more than 150, 2-D digital seismic lines, tied to ten wells and indicates the presence of canyon fill deposits. The oblique and sigmoidal prograding forsets of forth order cycles show rapid progradational infilling. Detailed mapping of the area suggests the presence of at least 3 entry points for the sediments apparently fed by rivers to the North and Northwest. A combination of chronostratigraphic charts, lithostratigraphic data, and structural style support the presence of turbidites in the area. Basinward, higher amplitude/continuous reflectors at the base of prograding clinoforms may correspond to turbidite systems. The southern most part of the Port Elizabeth trough appears to be the most prospective area for deep water sand reservoir accumulation. Relatively well defined and mounded seismic reflectors in the area, in addition to the blocky character of the gamma ray logs for the same interval in the wells, are interpreted as slope fan and/or basin floor fan deposits. Structural analysis indicates the basin is dissected by a series of NW-SE trending faults whose movement may have induced hydrocarbon migration in the area. The proximity of Agulhas/Falkland Fracture Zone has resulted in complex structural trap configurations combined with 4th Order sedimentary Cycles similar to Aptian/Albian Cycles in Arabia.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas