Formation mechanisms of low-magnesium calcite and associated barite at cold seeps in today's aragonite sea

低镁方解石（LMC）和重晶石的复合已在一些现代渗漏沉积中被报道，但这种共生在今天的文石海的形成条件仍然很不受约束。该项目旨在描述墨西哥湾现代渗漏中这种不寻常共生的形成环境。我们假设，重晶石和LMC的沉淀是由渗出液的组成，与盐水渗漏有利于矿物共生，这是罕见的浅海底在现代渗漏比墨西哥湾的其他地方。通过有机（脂类生物标志物）和无机地球化学（微量金属; S、O、C稳定同位素）重建有利于重晶石和LMC形成的渗漏流体的组成。这一方法将得到大麦哲伦星云铀系年龄测定的补充，并将使用过去形成重晶石和大麦哲伦星云的间歇活动渗漏的孔隙流体成分的现有数据。一套全面的低温地球化学方法的应用，将导致建立新的代理，将允许识别渗漏相关的重晶石和相关的LMC在其他地方。获得这些知识将是重建导致古生代全球分布的块状重晶石形成的环境条件的先决条件。至少有一些古生代重晶石矿床具有假定的渗漏专性动物群。一个更好的重建有利于重晶石形成在古生代的浅海底环境，从而促进识别的因素，控制早期演化的化学合成为基础的生态系统在渗漏。

Composite low-magnesium calcite (LMC) and barite have been reported from some modern seep deposits, but the formation conditions of this paragenesis in today's aragonite sea remain largely unconstrained. This project aims to characterize the formation environments of this unusual paragenesis at modern seeps in the Gulf of Mexico. We hypothesize that the precipitation of barite and LMC is governed by the composition of seep fluids, with brine seepage favoring a mineral paragenesis that is rare in the shallow subseafloor at modern seeps elsewhere than in the Gulf of Mexico. The composition of seep fluids that favored barite and LMC formation will be reconstructed by means of organic (lipid biomarkers) and inorganic geochemistry (trace metals; S, O, C stable isotopes). This approach will be complemented by uranium-series age dating of LMC and will use existing data on pore fluid composition of the intermittently active seeps where barite and LMC formed in the past. The application of a comprehensive set of methods of low-temperature geochemistry will lead to the establishment of new proxies that will allow for the recognition of seep-related barite and associated LMC elsewhere. Obtaining such knowledge will be the prerequisite for the reconstruction of the environmental conditions that led to the formation of globally distributed massive barite in the Paleozoic. At least some of the Paleozoic barite deposits bear putative seep obligate fauna. A better reconstruction of the shallow subseafloor environments that favored barite formation in the Paleozoic will consequently foster the identification of the factors that governed the early evolution of chemosynthesis-based ecosystems at seeps.