Ideal Seismic Reflection Site Survey of Lake Edward, Uganda and Zaire, East African Rift

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9710146 Scholz This program is a core project of IDEAL, the International Decade for the East African Lakes. The project will conduct an intermediate-resolution seismic reflection site survey of Lake Edward, in the northern part of the western branch of the East African Rift, in anticipation of subsequent drilling. The primary goal of the drilling program is to chronicle a quantitative high- resolution paleoclimate and paleolimnological history of the basin and surrounding region at 0o-1o S latitude on the East African plateau, extending back through at least two glacial-interglacial cycles. Ancillary goals include answering fundamental questions in the ares of extensional tectonics, and evolutionary biology and macroecology in continental rifts. The principal objectives of this seismic-reflection pre- drilling site survey are to 1) develop a robust sequence- and chron-stratigraphic framework for the upper 1000, of sedimentary section in this half-graben basin, 2) acquire a grid of high- quality, intermediate-resolution multichannel and single-channel seismic reflection data for siting one or more drill holes in the basin, 3) characterize the deformational fabric of the uppermost crust, and 4) determine the total sediment thickness and depth to syn-rift basement in the basin. Important issues to be considered through interpretation of the seismic data set include developing a relative lake level curve for the basin; determining which areas of the lake are likely to contain continuous stratigraphic records; and assessing the intrabasinal deformational fabric for helping determine extension direction in the East African Rift. Integrating the seismic data with the drill hole data sets will permit the development of quantitative, high-resolution models of lacustrine rift basin evolution. Since the primary drilling objectives are focused toward paleoclimate studies and limited to 100-500 m, and a vessel must be transported to the lake for the survey, an intermediate-resolution survey will be carried out using a small air gun seismic source and a short (300-600 m) seismic streamer, to acquire ~ 1500 km of data and image to a depth of ~ 1000 m. ***