New palaeogeographic and lake-level reconstructions of Lake Tanganyika: implications for tectonic, climatic and biological evolution in a rift lake

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 di ers profoundly from the classic Van Houten cycles of some Newark Supergroup rift basins. This di erence 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 midto 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. Tanganyika is the largest, and probably the oldest extant INTRODUCTION lake of the East African Rift System (Fig. 1A). The Palaeogeographic and lake-level reconstructions have palaeogeographic synthesis of Northern Lake Tanganyika proven to be immensely valuable tools in visualizing lake presented here is based on several prior reflection seismic histories and evaluating alternative hypotheses of palaeosurveys and coring studies (Tiercelin & Mondeguer, hydrology and palaeoclimate (e.g. Teller, 1985; Morrison, 1991; Bouroullec et al., 1991; Cohen et al., 1993a), also 1991). Because of the important role that many large, discussed in detail in the companion paper to this article tectonically formed lakes have for biological evolution, (Lezzar et al., 1996), as well as on outcrop and oil wells such reconstructions have considerable potential to studies from the region (Attou, 1988). resolve important debates among evolutionary biologists as well (e.g. Owen et al., 1990). However, the use of METHODS lacustrine reconstructions in this application has been much more limited. In this paper we present a series of Seismic stratigraphy and age estimations palaeogeographic reconstructions for Northern Lake The data and interpretations that we present here are Tanganyika with important implications for the tectonic, climatic and biological evolution of this rift basin. Lake based primarily on results from Project CASIMIR’s 1992 © 1997 Blackwell Science Ltd 107