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Seismic records of late Pleistocene aridity in Lake Tanganyika,tropical East Africa
Authors:Michael M McGlue  Kiram E Lezzar  Andrew S Cohen  James M Russell  Jean-Jacques Tiercelin  Anna A Felton  Evelyne Mbede  Hudson H Nkotagu
Institution:(1) Department of Geosciences, The University of Arizona, 1040 East Fourth Street, Tucson, AZ 85721, USA;(2) Department of Geological Sciences, Brown University, 342 Brook Street, Box 1846, Providence, RI 02912, USA;(3) UMR 6118 Géosciences-Rennes CNRS, Université de Rennes1, Campus de Beaulieu, 35042 Rennes Cedex, France;(4) Department of Geology, University of Dar es Salaam, Dar es Salaam, Tanzania
Abstract:New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences (A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity. Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged aridity.
Keywords:Lake Tanganyika  Lowstand  Paleolimnology  Rift-valley lake  Seismic stratigraphy  Tropical paleoclimate
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