COMPARATIVE SEQUENCE STRATIGRAPHY OF LOW-LATITUDE VERSUS HIGH-LATITUDE LACUSTRINE RIFT BASINS - SEISMIC DATA EXAMPLES FROM THE EAST-AFRICANAND BAIKAL RIFTS

Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modern examples of lacustrine rift b asins. All the rift lakes are segmented into half-graben basins, and s eismic reflection datasets reveal how this segmentation controls the f illing of the rift basins through time. In the early stages of rifting , basins are fed primarily by flexural margin and axial margin drainag e systems, At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by r ift shoulder uplifts, and sediment flux into the basins is concentrate d at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in h igh-latitude Lake Baikal. Lake levels are extremely dynamic in the tro pical lakes and in low-latitude systems in general because of the pred ominance of evaporation in the hydrologic cycle in those systems. Evap oration is minimized in relation to inflow in the high-latitude Lake B aikal and in most high-latitude systems, and consequently, major seque nce boundaries tend to be tectonically controlled in that type of syst em. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high- latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations. (C) 1998 Elsevier Science B.V. All rig hts reserved.