Browsing by Author "Qiang, Jin"

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    Origin and source characterization of methane in the shallow-water environment of Southern Lake Tanganyika Rift Basin, Tanzania
    (Current Science Association, 2021) Bishanga, Januarius Matata; Qiang, Jin
    Lake Tanganyika, located in the western part of Tanzania between 3°S and 9°S lat, harbours hydrocarbon and non-hydrocarbon gases in its northern and southern shallow-water environment. In this study, a geochemical analysis of stable carbon and hydrogen isotopes and an interpretation of individual gas molecular composition were done in order to determine the origin and composition of the naturally occurring hydrocarbon gases in Tanganyika Basin. Nitrogen, a non-hydrocarbon gas is a major component (76.69%–78.31%) by volume percentage followed by methane (11.68%–12.94%) and other higher hydrocarbons (0.16%–1.63%). The isotopic composition of carbon δ 13C1 and hydrogen δ DC1 ranges from –65.32‰ to –65.81‰ and –272.5‰ to –275.9‰ respectively. The isotopic compositions of ethane (δ DC2 = –36.7‰ to –35.2‰) and propane (δ DC3 = –31.3‰ to –27.5‰) reflect the thermogenic origin of these higher hydrocarbons. According to molecular characterization of carbon and hydrogen isotope ratios and δ D-values, methane gas falls in the biogenic origin category and is formed by carbon dioxide reduction. The isotopic composition of CO2 varies between –8.6‰ and –3.4‰. CO2 reduction is also regarded as a mechanism of biogenic methane formation based on carbon isotope fractionation factors (greater than 0.16).
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    Trace and rare earth element geochemistry of organic-rich sediments in the lacustrine Rukwa rift basin, Tanzania: implications for paleoproductivity, paleosalinity, and redox conditions
    (Springer Nature, 2021) Bishanga, Januarius Matata; Qiang, Jin
    Coal and mudstone beds in the Namwele coalfield, lacustrine Rukwa rift basin belong to the Late Carboniferous to Early Permian age. However, their origin, depositional environment, and organic matter enrichment in such a setting have not been well studied. In this study, samples were collected from the field outcrops and analyzed for their hydrocarbon generation potential, trace element (TE), and rare earth element (REE) proxies to examine their origin, paleoproductivity, organic matter enrichment, paleosalinity, and redox conditions. The results show that the total organic contents (TOC) of the investigated samples range from 3.74 to 13.6%, with an average of 7.21%. The anomalous TOC is a proof that sediments deposited in an oxic condition and low sedimentation rate. Concentrations and ratios of various redox indicators such as vanadium, nickel, copper, chromium, uranium, and thorium (V/Cr, V/(V + Ni), Ni/Co, and U/Th) suggest that the organic-rich sediments had strong terrestrial organic matter input and deposited under oxic conditions. The TOC versus redox ratios show negative correlation coefficients proving that oxic conditions are not suitable for organic matter preservation. According to the boron/gallium (B/Ga) ratio, water salinity ranges between 0.2 and 4.15 during sedimentation, indicating a freshwater environment. The more significant content of the trace elements Ni and Cu implies a high flux of organic matter. Lanthanum/ytterbium (La/Yb)n ratio is an indicator for characterizing different enrichment levels between light REE and heavy REE. The results show that samples are enriched in light REE, with (La/Yb)n, indicating a low sedimentation rate. These findings contribute to studies of the same sedimentary environment settings and further extend our knowledge of the potential organic-rich resources in the Rukwa rift basin.