Palaeogeographic and lake‐level reconstructions provide powerful tools for evaluating competing scenarios of biotic, climatic and geological evolution within a lake basin. Here we present new reconstructions for the northern Lake Tanganyika subbasins, based on reflection seismic, core and outcrop data. Reflection seismic radiocarbon method (RSRM) age estimates provide a chronological model for these reconstructions, against which yet to be obtained age dates based on core samples can be compared. A complex history of hydrological connections and changes in shoreline configuration in northern Lake Tanganyika has resulted from a combination of volcanic doming, border fault evolution and climatically induced lake‐level fluctuations. The stratigraphic expression of lake‐level highstands and lowstands in Lake Tanganyika is predictable and cyclic (referred to here as Capart Cycles), but in a pattern that differs profoundly from the classic Van Houten cycles of some Newark Supergroup rift basins. This difference results from the extraordinary topographic relief of the Western Rift lakes, coupled with the rapidity of large‐scale lake‐level fluctuations. Major unconformity surfaces associated with Lake Tanganyika lowstands may have corresponded with high‐latitude glacial maxima throughout much of the mid‐ to late Pleistocene.
Rocky shorelines along the eastern side of the present‐day Ubwari Peninsula (Zaire) appear to have had a much more continuous existence as littoral rock habitats than similar areas along the north‐western coastline of the lake (adjacent to the Uvira Border Fault System), which in turn are older than the rocky shorelines of the north‐east coast of Burundi. This model of palaeogeographic history will be of great help to biologists trying to clarify the evolution of endemic invertebrates and fish in the northern basin of Lake Tanganyika.
We present here the initial results of a high‐resolution (sparker) reflection seismic survey in Northern Lake Tanganyika, East African Rift system. We have combined these results with data from earlier multichannel reflection seismic and 5‐kHz echosounding surveys. The combination of the three complementary seismic investigation methods has allowed us to propose a new scenario for the late Aliocene to Recent sedimentary evolution of the North Tanganyika Basin. Seismic sequences and regional tectonic information permit us to deduce the palaeotopography at the end of each stratigraphic sequence. The basin history comprises six phases interpreted to be responses to variations in regional tectonism and/or climate. Using the reflection seismic‐radiocarbon method (RSRM), the minimum ages for the start of each phase (above each sequence boundary) are estimated to be: ?7.4 Ma, ? 1.1 Ma, ?393–363 ka, ?295–262 ka, ? 193–169 ka, ?40–35 ka. Corresponding lowstand lake elevations below present lake level for the last five phases are estimated to have been: ?650–700 m, ?350 m, ?350 m, ?250 m and ? 160 m, respectively. The latest phase from ?40–35 ka until the present can be subdivided into three subphases separated by two lowstand periods, dated at ?23 ka and ? 18 ka. From the late Miocene until the mid Pleistocene, large‐scale patterns of sedimentation within the basin were primarily controlled by tectonism. In contrast, from the mid Pleistocene to the present, sedimentation in Lake Tanganyika seems to have responded dramatically to climatic changes as suggested by repeated patterns of lake level fluctuations. During this period, the basin infill history is characterized by the recurrent association of three types of deposits: ‘basin fill’ accumulations; lens‐shaped ‘deep lacustrine fans’; and ‘sheet drape’ deposits. The successive low‐lake‐level fluctuations decreased in intensity with time as a consequence of rapid sedimentary filling under conditions of declining tectonic subsidence. The climate signal has thus been more pronounced in recent sedimentary phases as tectonic effects have waned.
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