Sedimentological Characteristics and Origins of Diatomaceous Deposits in the East African Rift System
Richard B. Owen, 2002. "Sedimentological Characteristics and Origins of Diatomaceous Deposits in the East African Rift System", Sedimentation in Continental Rifts, Robin W. Renaut, Gail M. Ashley
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Lacustrine diatomaceous deposits are widespread in the East African Rift System, occurring in Miocene to Holocene sedimentary units. Problems in their classification can be clarified with a common set of well-defined terms, including: diatomite, siliciclastic diatomite, subdiatomite, diatominc, and diatom-poor. Additional descriptors refer to lamination, fragmentation, and dissolution. Diatom taphonomy and assemblage alteration reflect sedimentation, interface, and analysis controls, including: dissolution, settling rates, fragmentation, and floral mixing. The spatial and temporal distribution of East African diatomaceous deposits, especially in the Kenya and Malawi Rifts, suggest specific models for the development of a variety of diatomaceous facies. The models are based on factors that control the availability of diatom nutrients, including: fluvial inputs, water depth, seasonality of rainfall, wind regimes and their influence on upwelling and overturn, and turbidity currents. In turn, these factors reflect tectonic and geomorphic setting, drainage basin geology and resultant water chemistry, and climatic setting.
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Continental rift basins have long been of interest to sedimentologists. Of all the terrestrial settings, rift basins typically provide the greatest accommodation space, and consequently have some of the longest records of continental sedimentation. These records are a product of a complex interplay between several factors that include geological structure and tectonic activity, volcanism, climate and its temporal variability, hydrology, biology and time. Sedimentation in Continental Rifts is a timely update on this exciting interdisciplinary field and presents new approaches and insights into tectonic and structural controls of sedimentation. Other topics included are lacustrine and fluviatile depositional environments and some lesser-known settings, such as springs, wetlands, and paleosols. Several papers consider the behavior of silica in rift lakes, particularly the roles of microorganisms in silica precipitation, whereas others examine the paleoenvironmental importance of freshwater carbonates. The contents of the volume show that sedimentological research in rift basins has progressed beyond basic facies description and general models, and is now focused on understanding the integrative effects of physical, chemical and biological processes in rifts.