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      Geochemical Characteristics of the Trace and Rare Earth Elements in Reef Carbonates from the Xisha Islands (South China Sea): Implications for Sediment Provenance and Paleoenvironment

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          Based on the concentrations of the trace elements, rare earth elements (REE), and Sr isotopic compositions in reef carbonates from the well ‘Xike-1’ reef core of the Xisha Islands, the constraints on sediment provenance and paleoenvironment were defined. Variations of the terrigenous input into the paleoseawater were traced in detail and the paleoenvironment and sediment provenance were further investigated. The results show that the HREE/LREE values in the reef carbonates are negatively associated with their Th and Al concentrations; however, their Al and Th concentrations show positive correlation. The lowest 87Sr/ 86Sr values in the reef carbonates generally coincide with the lowest values of Al, Th concentrations and the highest values of HREE/LREE. These data indicate that the HREE/LREE, Al concentrations, and Th concentrations of the reef carbonates are useful indexes for evaluating the influence of the terrigenous inputs on the seawater composition in the study area. From top to bottom, the changing process of the HREE/LREE values and Al, Th concentrations can be divided into 6 intervals; they are H1 (0–89.30 m, about 0–0.11 Myr), L1 (89.30–198.30 m, about 0.11–2.2 Myr), H2 (198.30–374.95 m, about 2.2–5.3 Myr), D (374.95–758.40 m, about 5.3–13.6 Myr), L2 (758.40–976.86 m, about 13.6–15.5 Myr), and H3 (976.86–1200.00 m, about 15.5–21.5 Myr). Moreover, the changing trend of the HREE/LREE values coincides with that of the seawater δ 13C values recorded by benthonic foraminiferal skeletons from the drill core of ODP site 1148 in the South China Sea (SCS), but not with that of the seawater δ 18O values. The high uplifting rates of the Qinghai-Tibet Plateau coincide with the high Th and Al concentrations and the low HREE/LREE values in the reef carbonates. These data indicate that the main factors controlling the changes of terrigenous flux in the SCS are the tectonic activities associated with Qinghai-Tibet Plateau uplifting and the variations of uplifting rates rather than paleoclimatic changes.

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          Most cited references 46

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          The geochemistry of redox sensitive trace metals in sediments

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            Evolution of the Ratio of Strontium-87 to Strontium-86 in Seawater from Cretaceous to Present

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              Neoproterozoic variations in the C-isotopic composition of seawater: stratigraphic and biogeochemical implications.

               A. Kaufman,  A. Knoll (1995)
              The recent proliferation of stratigraphic studies of delta 13C variation in carbonates and organic C in later Neoproterozoic and basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend in the C-isotopic composition of surface seawater. Alone, this trend does not adequately characterize discrete intervals in Neoproterozoic time. However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions. Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian. Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone. Isotopic data place strong constraints on the chemical evolution of seawater, linking it to major tectonic and paleoclimatic events. They also provide a biogeochemical framework for the understanding of the initial radiation of macroscopic metazoans, which is associated stratigraphically, and perhaps causally, with a global increase in the burial of organic C and a concomitant rise of atmospheric O2.

                Author and article information

                Journal of Ocean University of China
                Science Press and Springer (China )
                12 November 2019
                01 December 2019
                : 18
                : 6
                : 1291-1301
                1Key Laboratory of Submarine Geosciences and Prospecting Techniques, Ministry of Education, College of Marine Geosciences, Ocean University of China, Qingdao 266100, China
                2Zhanjiang Branch Institute of China National Offshore Oil Corporation (CNOOC) Limited, Zhanjiang 524057, China
                3North China Sea Environmental Monitoring Center, Ministry of Natural Resources, Qingdao 266033, China
                Author notes
                *Corresponding author: ZHAI Shikui
                Copyright © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2019.

                The copyright to this article, including any graphic elements therein (e.g. illustrations, charts, moving images), is hereby assigned for good and valuable consideration to the editorial office of Journal of Ocean University of China, Science Press and Springer effective if and when the article is accepted for publication and to the extent assignable if assignability is restricted for by applicable law or regulations (e.g. for U.S. government or crown employees).

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