DELTAIC SEDIMENTATION IN A RIFT-VALLEY LAKE - NEW SEISMIC-REFLECTION DATA FROM LAKE MALAWI (NYASA), EAST-AFRICA

Digital seismic reflection data acquired over the subaqueous parts of five rift-lake deltas in Lake Malawi (Nyasa), Africa, reveal a striking variability in delta morphology. Gross variations appear to be controlled by tectonic setting. Border-fault margin and accommodation-zone margin deltas have steeply sloping depositional surfaces, acoustic signatures dominated by chaotic seismic facies, and an overall aggradational character. Shoaling margin deltas that are opposite the main border faults and axial-margin deltas that parallel the rift axis have slopes generally < 1-degrees, are dominated by continuous reflections, and display distinctive progradational character. Lake-level fluctuations on the order of hundreds of metres have severely modified each delta.