Hydrocarbon Implications of Karoo Supergroup Turbidites and Tectonics in Northern Zimbabwe

TROMP, PAUL L., University of Zimbabwe, Harare, Zimbabwe

Field research in the relatively unstudied Lower Zambezi trough of northernmost Zimbabwe and adjacent Zambia and Mozambique has revealed a sedimentary tectonic history unlike other Karoo basins (Late Carboniferous to Early Jurassic) of the region. This presents a much better setting for petroleum deposits than has been found in those other areas. Aerial photo interpretation and reconnaissance geophysical data show strike-slip folds and faults at the surface and subbasins up to 10 km deep. This contrast with other Karoo basins, which are of a half-graben genesis, is further evident in the sedimentary sequences of the Lower Zambezi basin complex. Lacustrine turbidites occur in the Lower Karoo Kondo Pools Formation. Upper fan facies of a restricted active margin subaqueous fan system are found in limited outcrops in an accommodation zone uplift between the two subbasins. The overlying units are classical Karoo alluvial layers, but intercalated with a higher frequency of unconformities. Syndepositional and postdepositional deformation includes thrust faulting and detachment.

Hydrocarbon potential is enhanced by three virtues that are lacking in other parts of southern Africa. Distal facies to those seen in exposures of the Kondo Pools Formation subaqueous fans should be rich in sapropelic mudstone, the source rock so elusive elsewhere. Second, basin depth is sufficient for thermal maturity. Finally, the tectonic regime was conducive to the formation of convex as well as unconformity traps. Mobil Oil is in the midst of an exploration program that may capitalize on these factors.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)