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Sedimentary geochemistry of deepwater slope deposits in southern Lake Tanganyika (East Africa): Effects of upwelling and minor lake level oscillations
Journal of Sedimentary Research ( IF 2 ) Pub Date : 2022-08-31 , DOI: 10.2110/jsr.2021.104
Michael M. McGlue, Geoffrey S. Ellis, McKenzie A. Brannon, Jennifer C. Latimer, Jeffery R. Stone, Sarah J. Ivory, Neema E. Mganza, Michael J. Soreghan, Christopher A. Scholz

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-year-long 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.

中文翻译:

坦噶尼喀湖南部(东非)深水斜坡沉积物的沉积地球化学:上升流和小湖水位振荡的影响

坦噶尼喀湖是了解古代热带裂谷中碳质沉积物沉积过程的最有价值的现代类似物之一。先前对坦噶尼喀湖的研究强调了底水缺氧、沉积过程(半远洋沉降与重力流)和大规模(100 米)湖水位变化对沉积有机质含量质量的重要性。在这里,将相分析和许多有机地球化学工具(元素、碳同位素和程序热解)应用于坦噶尼喀湖南部的放射性碳测年岩心,以研究受高频气候波动影响的深水斜坡环境中碳质沉积物的积累伴随着轻微的(10 米)湖水位变化。岩相和地球化学的相当大的可变性是长达 1030 年的核心记录的特征,主要由气候介导的湖泊上升流系统变化驱动。平均总有机碳 (TOC) 浓度和氢指数分别为 6.9 wt.% 和 385 mg 碳氢化合物/g TOC 的层状硅藻渗出物和腐泥是在强烈上升流和多变水位期间沉积的沉积物的特征。通过重力流过程沉积的粉质沉积物同样富含有机物,这可能是由于保护性增强的底水缺氧。重新加工的火山灰稀释是研究地点有机浓缩的主要限制因素。
更新日期:2022-08-24
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