东沙海区浅层沉积物中黄铁矿异常及其意义

Authigenic Pyrites from the Shallow Sediments in Dongsha Area of South China Sea:Implications for Gas Hydrates Occurrence

东沙海区浅层沉积物的两个岩心出现大量的黄铁矿。GC10岩心中的黄铁矿在300 cm以下含量增加,在700 cm的区段达到最高,主要为管状、棒状、莓球状;HD319岩心黄铁矿则相对较低,只在最底部730 cm的区段突然增加,以莓球状为主。GC10岩心黄铁矿含量异常层位与甲烷含量增加层位一致,而在C_(org)-S_(sulfide)^(2-)含量变化图上,S^(2-)含量与有机碳含量线性关系不明显,显示了该岩心黄铁矿的形成主要受高甲烷流通量影响;而HD319岩心的有机碳高的层位,S^(2-)含量也高,表明HD319岩心黄铁矿的形成与沉积物中有机质降解密切相关。GC10岩心黄铁矿的δ^(34)S(‰)值在-17.149～-33.240 CDT之间,显示了非常负的硫同位素比值和宽的区间;HD319的δ^(34)S(‰)值-36.363～-39.162 CDT之间,相对比较稳定。GC10岩心黄铁矿的δ^(34)S(‰)值特征,可能与富甲烷环境有关,而HD319受其影响稍弱。

A great deal of pyrites is found in two cores from Dongsha area of South China Sea. The amount of pyrites in the core GC10 increase below 300cmbsf, and reach the maximum in 700cmbsf. Pyrites mainly occur in the form of tube and fraimboid. In the core HD319, pyrites rarely occur above 730cmbsf but boom below the 730cmbsf in the form of fraimboid. For GC10, it -- Ssulfide due to shows no clear relation between pyrites sulfur and organic carbon in the plot of C org 2- the pyrites forming in the high flux of upward between pyrites sulfur and organic carbon in the methane. There is a good positive correlation --Ssulfide of the core HD319, showing plot of C ors 2- the influence of organic matter decomposition on pyrites formation. The values of δ34 S‰ of pyrites in the core GC10 rang from - 17. 149‰CDT to -33.240‰CDT, and that of the core HD319 vary between -36. 363‰CDT and -39. 162‰CDT. The isotopic composition of pyrites suggest that pyrites in the core GC10 form under the influence of strong methane flow which probaly derived from gas hydrates dissociation, but pyrites in the core HD319 mainly result from organic matter decomposition.