Mineralogy and stable isotopic composition of authigenic carbonate samples from Chapopote TVG-6

The Campeche Knolls in the Bay of Campeche, southern Gulf of Mexico, were investigated through detailed seafloor mapping, ROV surveys, and sediment and pore water sampling. The knolls are elongated, submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor. Several of the knolls are associated with sea-surface oil slicks identified from satellite data, indicating the presence of hydrocarbon seeps on the seafloor. One of the knolls, named "Chapopote", was studied in detail during two international research expeditions (SO174/2 and M67/2) and is characterized by extensive hydrocarbon seepage including large asphalt flows, oil and gas seeps, and seafloor gas hydrate deposits. Chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward-diffusing seawater and hydrocarbon-rich pore fluids at shallow sediment depth. Authigenic carbonates are characterized by aragonite, exhibit a porous texture, and are cemented by a matrix of microsparitic to sparitic aragonite. Macropores of the carbonates were completely filled with liquid oil. Carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism. Banded/botryoidal aragonite cements line the intra- and bioclasts and incompletely fill the pore spaces. The stable carbon isotopic composition of authigenic aragonite varies between -28.6 per mill and -17.9 per mill (PDB), identifying oil oxidation as the primary source of carbon to the DIC pool, while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane (AOM). These observations indicate the presence of additional, AOM-independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the Gulf of Mexico basin. Oxygen isotope data of authigenic aragonite vary from + 2.5 per mill to + 3.8 per mill (PDB), indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids.

墨西哥湾南部坎佩切湾的坎佩切海丘（Campeche Knolls）通过详细的海底测绘、遥控无人潜航器（Remotely Operated Vehicle，ROV）调查以及沉积物和孔隙水采样开展了研究。该类海丘为盐构造作用形成的拉长状海底丘陵，相对周围海底的正地形高差可达800米。多座海丘与卫星数据识别出的海面浮油相关联，表明海底存在烃类渗漏活动。其中一座名为“查波波特（Chapopote）”的海丘在两次国际科考航次（SO174/2与M67/2）中被详细研究，其特征为广泛的烃类渗漏，包括大规模沥青流、油气渗漏以及海底天然气水合物沉积物。化能自养生物群落与自生碳酸盐（authigenic carbonate）沉积伴随渗漏活动分布，其形成源于生物地球化学循环，以及浅沉积物层内向下扩散的海水与富烃孔隙流体的相互作用。自生碳酸盐以文石（aragonite）为主要组分，具有多孔结构，由微亮晶至亮晶文石基质胶结。碳酸盐的大孔隙完全被液态石油充填。碳酸盐微组构包括球粒状或团块状组构，这可能指示了由微生物代谢形成的微环境的存在。条带状/葡萄状文石胶结物分布于内碎屑和生物碎屑内部，并不完全充填孔隙空间。自生文石的稳定碳同位素组成介于-28.6‰至-17.9‰（PDB标准），表明石油氧化是溶解无机碳（Dissolved Inorganic Carbon，DIC）库的主要碳来源；而脂质生物标志物数据则证实了负责甲烷厌氧氧化（Anaerobic Oxidation of Methane，AOM）的微生物群落同时存在。上述观测结果表明，墨西哥湾盆地的烃类渗漏点还存在其他不依赖甲烷厌氧氧化的碳固存反应，同时也展现了该盆地渗漏点生物地球化学过程的复杂性。自生文石的氧同位素组成介于+2.5‰至+3.8‰（PDB标准），指示碳酸盐沉淀与周围孔隙流体处于轻微的不平衡状态。