| Qingdao Institute of marine geology, China Geological Survey | Host |
| Citation: |
WU Daidai, XIE Rui, YANG Rui, SUN Tiantian, YANG Fei, LIU Lihua, WU Nengyou. GEOCHEMISTRY OF THE SEDIMENTS IN SHENHU HYDRATE DRILLING AREA, NORTHERN SOUTH CHINA SEA[J]. Marine Geology & Quaternary Geology, 2017, 37(6): 100-109. doi: 10.16562/j.cnki.0256-1492.2017.06.011
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GEOCHEMISTRY OF THE SEDIMENTS IN SHENHU HYDRATE DRILLING AREA, NORTHERN SOUTH CHINA SEA
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Abstract
The formation and decomposition of gas hydrate as well as the methane leakage caused by associated biogeochemical processes may change the depositional environment of the seabed. To identify the decomposition of hydrate as well as the change in marine environment caused by the seeping methane will contribute to the understanding of the processes of hydrate formation and decomposition. In this paper, we selected the Core SH3 as a case from the Shenhu hydrate drilling area in the northern part of South China Sea to study the formation and deterioration of hydrate. Carbon and sulfur contents, main and trace elements, especially redox sensitive elements are measured. Data from pore water and previous researches are also studied. The study suggests that the sediments of the Shenhu area are mainly sourced from a fluvial origin with a little of loess and felsic igneous materials. From the data of U, Mo contents and U/Mo ratio, as well as carbon and sulfur contents, it is inferred that the layers at 10~25 mbsf in the core of SH3 is mainly formed in a reduced depositional environment, resulted from sulfate reduction by the anaerobic oxidation of methane. The change in redox condition of depositional environment may lead to the fractionation of LREE/HREE and MREE/HREE in the layers. In the SH3 core sediment, there is a sub-oxidized depositional environment at the level of about 180~215 mbsf. It is supposed to be caused by the deposition of turbidites. The depositional environment of fine-grained sediments, at the same time, also leads to the fractionation of light and heavy rare earth elements. To sum up, we have succeeded in revealing material source, environment change in the Shenhu area and the specific role of hydrate-sedimentary environment in this paper and the results are very useful for understanding of the origin of gas hydrate.
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Keywords:
- the Shenhu area /
- hydrate drilling area /
- gas hydrate /
- sedimentary environment
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References
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WU Daidai, XIE Rui, YANG Rui, SUN Tiantian, YANG Fei, LIU Lihua, WU Nengyou. GEOCHEMISTRY OF THE SEDIMENTS IN SHENHU HYDRATE DRILLING AREA, NORTHERN SOUTH CHINA SEA[J]. Marine Geology & Quaternary Geology, 2017, 37(6): 100-109. doi: 10.16562/j.cnki.0256-1492.2017.06.011
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Figure 1.
Map showing the locations of the sediment core in this study
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Figure 2.
The contents of TN, TC, TS, TOC, TOC / TN and TOC / TS with depth of the sediment in the SH3 core
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Figure 3.
The changes in U, Mo, U / Mo, the ratios of U/Th and V/Sr with depth in the SH3 core sediments
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Figure 4.
The curve of Al/Ti, La/Sm, Zr/Y, and LREE/HREE, MREE/HREE ratios with depth in SH3 core
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Figure 5.
Variation in SO42- concentration with depth in SH3 pore water (a), and hydrate saturation with depth distribution in the SH3 Drilling core (b)
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Figure 6.
Distribution of Cr/V-Y/Ni and Co/Th-La/Sc phase diagrams for all samples in SH3 core
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Figure 7.
Comparison of the UCC (Upper Continent Crust) normalized distribution curve of the rare earth elements in the SH3 core sediments
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Figure 8.
Mixed diagram of LREEN/HREENand MREEN/HREEN