High-resolution seismic investigation of Lake Tana, northern Ethiopia

High-resolution single-channel seismic reflection data and sediment core samples from Lake Tana, Ethiopia, reveal a dynamic Holocene and late Pleistocene history of the lake. The seismic data show a sequence of sediments in excess of 45 m thick with four strong reflection horizons. The horizons are interpreted to be a consequence of climate conditions resulting in complete lake desiccation. The youngest of these surfaces, at a depth of 8–12 m beneath the present lake floor, is dated at about 17 k cal BP and is correlated with desiccation of Lake Victoria during Heinrich event 1. Similar surfaces were mapped at depths of approximately 25, 30 and 45 m below the lake floor, suggesting numerous late-Pleistocene lowstands. No features within the seismic sections suggest deep-water depositional environments. Deeply incised channel sequences cut through the near-surface sediments above the strong lake-wide reflection horizons and represent periods of significant erosion during the early Holocene. These events are tied to core intervals dated to 8.4 and 12.1 k cal BP, which also correspond to climate change during regional arid periods. On the northern lake margin, the geometry of sediment accumulation suggests recent faulting with associated continuing basin subsidence in this active tectonic region. The seismic and core data from Lake Tana can be summarized as showing a sedimentation history through the Holocene and late-Pleistocene that reflects the interplay between rapid climate change and long-term basin subsidence.