DETRITAL PALEO-RECORDS FROM LAKE TANGANYIKA: A PRELIMINARY EXAMINATION OF HORST AND PLATFORM ENVIRONMENTS

Lake Tanganyika is one of the world’s premier sites for recovering a complete Miocene-Recent sedimentary record of climate change for the African tropics through continental scientific drilling. The lake hosts diverse depositional settings that are strongly conditioned by patterns of structural deformation, to include isolated deepwater horsts and gently sloping flexural margin platforms marked by variable bathymetry, lake floor oxygen levels, wave energy, and patterns of deltaic or gravity-driven sedimentation. These settings are impacted by lake level change in different and complex ways, and as a result, understanding the sensitivity of paleo-indicators for recording key environmental dynamics requires rigorous calibration exercises. Although a number of different biogeochemical and molecular climate proxies have been investigated for Lake Tanganyika’s sediments, little attention has been given to siliciclastic particle size and clay minerals as indicators of depositional processes, weathering, and hydroclimatic change. Here, we report preliminary results on the detrital component of sediments collected from three settings in southern Lake Tanganyika: (1) the anoxic Kalya horst block (~600 m water depth); (2) the anoxic distal Kalya Platform (~330 m water depth); and (3) the Kitwe Platform both above and below the oxycline (< 795 m water depth). For the Kalya horst and platform, we developed a comparative downcore analysis of particle size trends. Accurate grain size analysis required repeated chemical digestions to remove biogenic and chemical sediments, plus careful examination of smear slides prior to analysis by laser diffraction. Late Quaternary aged sediments from the Kalya horst are largely unremarkable with respect to %sand and silt:clay patterns, whereas the distal Kalya platform has demonstrable variability in the amount of coarse particles deposited over this interval. Clay minerals have been analyzed in modern samples along depth transects on the Kitwe platform using standard x-ray diffraction methods. Initial results indicate the presence of smectite, kaolinite, chlorite and illite. Ongoing research will use insights gained from the modern clay mineral suite to further scrutinize and calibrate interpretations of clays minerals preserved in cores.