【摘要】 白云石成因一直是地学中尚未解决的难题,海底冷泉系统中发育的原生白云石为解决白云石成因问题提供了新途径。台湾甲仙白云仙谷早上新世盐水坑组页岩地层中发育有冷泉白云岩,其流体来源和沉积环境并不清楚。本文通过矿物学和岩石学,结合碳氧同位素、微量和稀土元素地球化学,探索该冷泉白云岩的流体特征和形成环境,为解决白云石成因提供参考。白云仙谷冷泉白云岩以烟囱状或透镜状产出于页岩中,碳酸盐矿物均为泥微晶白云石,含量为61.4%～88.0%。冷泉白云岩的δ13C为-27.08‰～-10.58‰,指示形成白云石的碳源可能是热成因甲烷和海水的混合。Ni/Co均值为12.54,稀土元素配分模式呈中稀土富集、无Ce异常,均表明冷泉白云岩形成于弱还原的沉积环境。在弱还原环境中的冷泉微生物的作用下,促进了HCO3-的增加和SO42-的消耗,可能有利于冷泉白云石的形成。更多还原

【Abstract】 The origin of dolomite is a long-term argument in geology. In recent years, protodolomite has been discovered in hydrocarbon seeps,which provides critical evidence for solving the problem. Therefore, the authigenic carbonate found in hydrocarbon seeps is regarded as a kind of unique geochemical archives of fluid seeping in history. The carbonates studied in this paper occur as chimneys or lenses within the shale of Early Pliocene, the Yanshuikeng Formation, exposed at Chiahsien, southwestern Taiwan. Petrological and geochemical tests, such as petrography, mineralogy, carbon and oxygen stable isotopes, and rare earth element(REE) compositions, are made to trace the fluid sources and sedimentary environment. X-ray analyses suggest that the carbonate is mainly composed of dolomite(61.4%～ 88.0%). The δ13 C values of dolomites range from-27.08‰ V-PDB to-10.58‰ V-PDB, suggesting a thermogenic methane and seawater associated carbon sources. The value of Ni/Co is around 12.54, and the original REE distribution shows a pattern of enrichment in the middle without Ce anomalies. All these results indicate that the Chiahsien dolomite was precipitated from reducing seep fluids. Under the action of microorganisms in the sub-reducing environment, HCO3-is increased and the SO42-more consumed, which is in favor of the formation of seep dolomites.更多还原