DELTAS OF THE LAKE MALAWI RIFT, EAST-AFRICA - SEISMIC EXPRESSION AND EXPLORATION IMPLICATIONS

High-resolution, air-gun-sourced seismic reflection surveys over the o ffshore regions of five river deltas in Lake Malawi in the East Africa n rift system reveal considerable variability in acoustic facies and s tratigraphic architecture. This variability can largely be attributed to the influences of different structural settings, and to a lesser de gree to high-amplitude (100-400 m) and high-frequency (1000 to 100,000 yr) fluctuations in lake level. Deltas on flexural and axial margins in the rift lake show well-developed progradational geometries. In con trast, a delta on a steep, accommodation zone margin distributes coars e sediments over a broad depositional apron, rather than concentrating sediment in discrete progradational lobes as on the other deltas. A l arge border fault margin river delta displays the most complex tectoni c and stratigraphic architecture of all the deltas studied. It contain s several delta-associated facies, including prograding clino-form pac kages, fan deltas stacked against a boundary fault, and extensive suba queous fans. Flexural margin lowstand deltas may be the most prospecti ve for hydrocarbon exploration due to their large, internally well-org anized, progradational lobes and their close proximity to deep-water, high total organic carbon lacustrine source facies.