QUATERNARY STRATIGRAPHY OF LAKE VICTORIA FROM NEW HIGH-RESOLUTION CHIRP SEISMIC REFLECTION DATA

Lake Victoria, East Africa, is the second-largest freshwater lake in the world and plays a significant role in the region's ecosystem and economy. Previous studies on the lake have established that changes to the lake’s environment have important implications for the evolution of the lake’s remarkable biodiversity and the broader context of African ecosystems, and that over a period of ~400 kyr or more, the lake may have repeatedly dried up and replenished. In January we acquired high-resolution Compressed High Intensity Radiating Pulse (CHIRP) seismic reflection data to investigate the Quaternary stratigraphy of Lake Victoria. A total of 1,250 km were collected in the south and east-central parts of the lake using an Edgetech 512 subbottom towfish operating at 0.5-7.5kHz. ­­Processed and conditioned data resulted in detailed images of the lacustrine stratigraphy to depths of ~45m. Estimates of depth to basement are made from legacy multi-channel seismic reflection data collected in 1995. The previously identified late-Pleistocene desiccation surface is a prominent feature of the new CHIRP data, and evidence for at least three older low-lake stages include subsurface paleodeltas and paleoshorelines. Those features suggest previous low lake stages at depths of 65, 69, and 83 m below modern lake level and contribute to our understanding of Lake Victoria’s hydroclimate in the Quaternary. This work facilitates drill site selections of the forthcoming Lake Victoria Scientific Drilling Project.