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

点击翻译按钮获取中文摘要

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.