Study on the Authigenic Pyrites and Their Sulfur Stable Isotopes in Recovered Sediments during IODP 311 Expedition

Abstract

Abstract:

To understand better the response of authigenic minerals in sediments of the gas hydrate system, total 652 sediment samples recovered from IODP 311 Expedition were washed and all authigenic pyrites were picked up. SEM photographs show that pyrites occurred in forms of both microspheroids and cubic crystal aggregations,caused by microbial fossilization and inorganic processes,respectively. The stable sulfur isotopic compositions seem to have a wide range of δ³⁴S_CDT values from -35.4‰ to +53.6‰ for the processes of anaerobic oxidation of methane(AOM).Sea salt sulfate in the upper part of sediment column was dominantly reduced by AOM, and the remained sulfate involving reduction would probably cause positive sulfur isotopic excursion of pyrites. In the cold vent theδ³⁴S_CDT values increase gradually with depth from-35.83‰ near the top sediment to 32.49‰ in deep, indicating that more remained sulfates once involved in reduction under higher methane flux and more intensive AOM. This study will have important impact on exploring the potential marine gas hydrate in China and on deciphering the ancient methane derived sedimentary records in the Earth history.

Key words: IODP 311 Expedition, sediment, authigenic pyrite, stable sulfur isotope

CLC Number:

P736.4

CHEN Qi, WANG Jia-sheng, WEI Qing, WANG Xiao-qin, LI Qing, HU Gao-wei，GAO Yu-ya. Study on the Authigenic Pyrites and Their Sulfur Stable Isotopes in Recovered Sediments during IODP 311 Expedition[J]. Geoscience, 2008, 22(3): 402-406.

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