Lake Tanganyika ranks among the most valuable modern analogs for understanding depositional processes of carbonaceous sediments in ancient tropical rifts. Prior research on Lake Tanganyika has emphasized the importance of bottom-water anoxia, depositional processes (hemipelagic settling versus gravity flows), and large-scale (100s of meters) lake level change on the quality of sedimentary organic matter content. Here, facies analysis and numerous organic geochemical tools (elemental, carbon isotope, and programmed pyrolysis) were applied to a radiocarbon-dated core from southern Lake Tanganyika to investigate the accumulation of carbonaceous sediments in a deepwater slope environment influenced by high-frequency climatic fluctuations accompanied by only minor (10s of meters) lake level changes. Considerable variability in lithofacies and geochemistry characterizes the ~ 1030-yearlong core record, chiefly driven by climate-mediated changes to the lake's upwelling system. Laminated diatom oozes and sapropels with mean total organic carbon (TOC) concentrations and hydrogen indices of 6.9 wt.% and 385 mg hydrocarbon/g TOC, respectively, characterize sediments deposited during periods of strong upwelling and variable water levels. Silty sediments deposited via gravity-flow processes were likewise rich in organic matter, likely due to preservation-enhancing bottom-water anoxia. Dilution by reworked tephra was the chief constraint on organic enrichment at the study site. Data from this study reveal that oscillations in atmospheric and limnological processes in the absence of major shoreline movements can result in geochemically diverse deepwater slope sediments, which have implications for improving depositional models of petroliferous continental rift basins.
|Original language||English (US)|
|Number of pages||18|
|Journal||Journal of Sedimentary Research|
|State||Published - 2022|
Bibliographical noteFunding Information:
Financial support was provided by the University of Kentucky-Pioneer Endowment, the Society of Exploration Geophysicists-Geoscientists without Borders (201401005), and the U.S. National Science Foundation (EAR-1424907). The authors thank the Tanzania Commission for Science and Technology for permitting (2016-300-ER-2011-87). Support in the field was provided by the Tanzania Fisheries Research Institute, the Nature Conservancy, J. Lucas, E. Ryan, A. Mbonde, M. Mupape, and the crew of the M/V Maman Benita. Core curation was provided by LacCore. Analytical assistance provided by J. Backus, E. Davis, A. Conner, J. Munizzi, R. Brown, H. Bierly, E. Smith, R. Gaines, and M. Dreier is gratefully acknowledged. We thank K. Marsaglia, J. Trabucho-Alexandre, J. Southard, C. Thomas, J. Flaum, B. Shaffer, and an anonymous reviewer for edits and comments that improved the quality of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Financial support was provided by the University of Kentucky–Pioneer Endowment, the Society of Exploration Geophysicists–Geoscientists without Borders (201401005), and the U.S. National Science Foundation (EAR-
© 2022, SEPM (Society for Sedimentary Geology).
Continental Scientific Drilling Facility tags