南海北部神狐水合物赋存区浅表层沉积物自生矿物特征及其成因探讨

The characteristics and formation mechanism of authigenic minerals in shallow sediments of Shenhu area,northern South China Sea

通过对南海北部神狐海域Site5B和Site4B站位岩心柱沉积物中自生矿物的类型、形貌特点、丰度和稳定同位素特征的研究,探讨了自生矿物的成因机制。研究表明,沉积物中主要发育黄铁矿和碳酸盐类自生矿物。两个站位中发育的自生矿物的丰度、分布位置、晶体形貌和个体大小等存在明显差异,可能与不同站位中甲烷通量和深部构造有关。自生黄铁矿可能是硫酸盐与甲烷等烃类气体或有机质的厌氧氧化作用的产物,极低负值的硫同位素值可能与硫酸盐还原菌和单质硫歧化菌共同参与有关。自生碳酸盐矿物的成因则相对复杂,其形成过程受多种因素的综合影响。碳同位素值未表现出极低负值,可能是甲烷、有机质和正常海水等碳源混合的结果。

Based on detailed researches on the species, abundances, crystal morphological features and stable C, O, S isotopes of the authigenic minerals in shallow core sediments of Site 5B and Site 4B within Shenhu area gas- hydrate potential deposits of northern South China Sea, the authors found that authigenic pyrites and carbonates are the dominating species in shallow sediments, and that great differences exist between Site 5B and Site 4B in abundance, distribution, morphology and grain size of pyrites and carbonates. Taking into account the same ge- ological background of both sites in Shenhu area, the authors have inferred that the great differences might be related to the local methane flux and deep structures in different sites. Authigenic pyrites might have been formed by the anaerobic oxidation of methane or organic matter with sulfate reduction. Extremely negative sul- fur isotope of pyrites might be related to the co-action of sulfate reduction bacteria and sulfur disproportionate bacteria- Authigenic carbonate was probably formed in a relatively complicated process, and carbon isotopic records might reflect mixed carbon sources of methane, organic matter and sea water.