Characteristics and Implications of Magnetic Susceptibility of Sediments in Core 08CF7 from the Baiyun Sag in Northern South China Sea

Abstract

Abstract:

Magnetic anomalies in marine sediments are related to methane venting and its products. In order to understand the characteristics of magnetic variability in sedimentary prism from the gas hydrate areas and their possible implication, magnetic susceptibility (MS) of 331 sediment samples in core 08CF7 from Baiyun sag in the northern South China Sea was investigated. MS values range from 5.54×10-6SI to 26.56×10-6SI with a mean value of 11.41×10-6SI. According to the colors and MS values of sediments, the susceptibility profile of core 08CF7 was divided into three different sedimentary layers, 0 to 188 cm，188 to 240 cm and below 240 cm, which were corresponded to the sulfidic zone, the transition zone between the sulfidic zone and the upper sulfate methane transition (SMT) and SMT, respectively. Our results indicate that sub-sea gas venting is responsible for the magnetic anomalies of sediments in core 08CF7. A possible mechanism is proposed:under the strongly reducing environments, HS-of AOM product reacts with Fe3+ in sediments, resulting in precipitation of paramagnetic pyrite. MS variability of marine sediments is feasible to estimate the occurrence and depth of SMT, which provides an indirect method to identification of gas hydrate below the seafloor in the northern slope of South China Sea.

Key words: magnetic susceptibility, pyrite, sulfatemethane transition, northern South China Sea

CLC Number:

TE132.2

CHEN Zhong, CHEN Han, YAN Wen, YAN Bin, XIANG Rong, LIU Jian-Guo. Characteristics and Implications of Magnetic Susceptibility of Sediments in Core 08CF7 from the Baiyun Sag in Northern South China Sea[J]. Geoscience, 2010, 24(3): 515-520.

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