Distinct sedimentary processes reflected in the isotopic signatures of dolomitic concretions in the Miocene Pohang Basin (southwestern East Sea) |
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| Authors: | Boo-Keun Khim Kyung Sik Woo Young Kwan Sohn |
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| Institution: | aDivision of Earth Enviromental System, Pusan National University, Busan 609-735, Republic of Korea;bDepartment of Geology, Kangwon National University, Chuncheon 200-701, Republic of Korea;cDepartment of Earth and Environmental Sciences, Gyeongsang National University, Jinju 660-701, Republic of Korea |
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| Abstract: | Dolomitic concretions in diatomaceous hemipelagic sediments of the Miocene Pohang Basin in the southwestern East Sea (Sea of Japan) preserve distinct signals of two independent sedimentary processes, which controlled the extents of isotopic compositions. Variable δ18O (−9.1‰ to +0.7‰) and high δ13C (+3.1‰ to +17.9‰) values suggest that the concretions formed in the methanogenic zone with alteration of the residual mid-Miocene seawater by volcanogenic sediments. Remarkable δ18O and δ13C values show a strong linear relationship, indicating that distinctly independent depositional processes operated during the formation of the concretions. The degree of methanogenesis was enhanced during rapid hemipelagic sedimentation of organic-rich particles, resulting in higher δ13C values, and the effect of volcaniclastics was diluted, maintaining the original properties of ambient mid-Miocene seawater. In contrast, lower δ18O and 87Sr/86Sr values characterize the effect of volcaniclastic sediments that were transported by intermittent gravity flows and interacted with mid-Miocene seawater. The input of volcaniclastic sediment probably degraded the role of methanogenesis by lowering the contents of organic matter and thereby decreased the δ13C values within the concretions. Isotopic signals recorded within the concretions highlight understanding of the depositional environment and evolution of the pore-water chemistry. |
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| Keywords: | Carbonate concretion Stable isotope Strontium isotope Depositional processes Miocene Korea |
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