Paper No. 309-4
Presentation Time: 8:55 AM
A ~10 MILLION YEAR HISTORY OF BASIN EVOLUTION IN LAKE TANGANYIKA RECORDED IN MULTIPLE VINTAGES OF SEISMIC REFLECTION DATA
Lake Tanganyika is the largest and oldest lake in Africa, and a freshwater system extant since the mid-Miocene. It is an excellent modern example of a magma-poor continental rift, and its >5 km-thick sedimentary section contains exquisite records of rifting, changing African climates, and evolving biodiversity. We present results from an integration of newly reprocessed basin-scale seismic reflection data, recently acquired commercial seismic reflection data, and legacy high-resolution seismic data from this active multi-segment rift system. Subsidence and extension in the Lake Tanganyika Rift is principally accommodated on nine major border faults, with additional extension accommodated on numerous intra-rift faults and faults outside the rift valley proper. Maximum sediment thickness is in excess of 3800 s TWTT in the center of the rift-lake. A sequence of reflections beneath the “Nyanja Event”, a widespread high-amplitude reflection visible at the base of the interpreted syn-rift section, may indicated earlier episodes of sedimentation, and perhaps extension, that predates the modern lake. The late-Cenozoic syn-rift section above the Nyanja Event is separated into six depositional sequences that reflect a ~10 million-year progression of extension, accelerating subsidence, and development of faulted relief, and overprinted by an increasingly variable climate in the late Neogene and Quaternary. Lower (older) sequences reflect an environment of low relief and shallow lacustrine or periodically fluvial conditions, whereas later sequences contain complex facies assemblages reflecting deep lacustrine environments, which in some areas are dominated by both mass transport and turbidity flow deposits. Syn-depositional fault analyses reveal that extensional strain within Lake Tanganyika during the Pleistocene has been primarily accommodated along border fault systems, which subsequently controlled recent basin morphology and sedimentation. Complex facies assemblages, mass transport deposits, and canyon incisions observed in Pleistocene depositional sequences are indicative of marked high-amplitude and high frequency shifts in hydroclimate, when water levels varied by as much as 600 m.