西藏南部浪卡子县桑秀组早白垩世腕足Peregrinella和伴生的自生碳酸盐岩的冷泉属性研究

The enigmatic Cretaceous brachiopod Peregrinella has become intriguing because of its distinctive morphology, its mass occurrence in isolated lenses and its extensive yet discontinuous paleogeographic distribution. The Peregrinella has been considered to be chemosymbiotic fauna which lived at chemosynthesis-based cold-seep environments. However, there is a lack of consensus. The occurrence of Peregrinella with authigenic carbonates within Sangxiu Formaiton, Nagarze County, Southern Tibet provides a unique opportunity to investigate association of Peregrinella with chemosymbiotic community. Here, the present project is designed to know the stable isotopic compositions of Peregrinella shells, and the sedimentological, petrographic, and stable isotopic characteristics of brachiopod Peregrinella-bearing chimney-like authigenic carbonates. The obtained data will also be used to determine whether the fluid compositions of the Peregrinella shells and the Peregrinella-bearing carbonates were mainly derived from cold seep systems. The aim of the project is to evaluate if Peregrinella lived in the cold seeps and belongs to chemosynthesis-based communities. Overall, the study will provide clues for studies of cold seeps and chemosymbiotic communities in the geological history.

早白垩世腕足Peregrinella化石群因其独特的形态，密集分布于透镜体，广泛但不连续的地理分布而受到广泛的关注。腕足Peregrinella被认为是冷泉专属的自养型生物。但是目前还未成为学术界的广泛共识。西藏南部浪卡子县工波学区舍朗日山北坡桑秀组发育有Peregrinella化石群和伴生的烟囱状的自生碳酸盐岩，为我们研究腕足Peregrinella的冷泉属性提供了绝佳的机会。本项目将通过研究腕足Peregrinella壳体的碳、氧同位素地球化学和伴生的自生碳酸盐岩的岩石学、矿物学及碳、氧同位素地球化学特征，判断形成Peregrinella壳体和伴生的自生碳酸盐岩的流体是否是冷泉流体，探索Peregrinella是否是发育于冷泉渗漏系统的自养型生物，为地质历史时期冷泉系统及其发育的自养型生物的判定提供思路。

早白垩世腕足Peregrinella化石群因其独特的形态，密集分布于透镜体，广泛但不连续的地理分布而受到广泛的关注。腕足Peregrinella被认为是冷泉专属的自养型生物。但是目前还未成为学术界的广泛共识。西藏南部浪卡子县工波学区舍朗日山北坡桑秀组发育有Peregrinella化石群和伴生的烟囱状的自生碳酸盐岩，为我们研究腕足Peregrinella的冷泉属性提供了绝佳的机会。在野外观察中，自生碳酸盐岩展现出结核状，透镜状和烟囱状。岩石学结果显示自生碳酸盐岩含丰富的胶结物和沥青质；同时，在发育自生碳酸盐岩的页岩地层之下的火成岩岩石发育气孔构造，这些孔洞被沥青质充填。自生碳酸盐岩碳同位素值的范围为-23.1‰到-6.8‰。这些特征显示自生碳酸盐岩为典型的冷泉成因，其流体成分是石油等烃类物质。另一方面，腕足Peregrinella壳体的碳同位素值范围为-0.3‰到1.0‰，与冷泉碳酸盐岩的碳同位素值显著不同，显示形成Peregrinella壳体的碳流体并不是来源于石油等烃类物质，而是来自海水。尽管形成Peregrinella壳体的碳流体并不是来源于冷泉流体，但是腕足类Peregrinella化石仅存在于石油渗漏相关的冷泉碳酸盐岩中，揭示Peregrinella更适应石油等烃类渗漏环境，是生存于冷泉渗漏系统中的自养型生物。