Cold‐water coral (CWC) mounds are build‐ups comprised of coral‐dominated intervals alternating with a mixed carbonate‐siliciclastic matrix. At some locations, CWC mounds are influenced by methane seepage, but the impact of methane on CWC mounds is poorly understood. To constrain the potential impact of methane on CWC mound growth, lipid biomarker investigations were combined with mineralogical and petrographic analyses to investigate the anaerobic oxidation of methane (AOM) and authigenic carbonate formation in sediment from a seep‐affected CWC mound in the Gulf of Cadiz. The occurrence of AOM was confirmed by characteristic lipids found within a semi‐lithified zone (SLZ) consisting of authigenic aragonite, high‐magnesium calcite and calcium‐excess dolomite. The formation of high‐Mg calcite is attributed to AOM, acting as a lithifying agent. Aragonite is only a minor phase. Ca‐excess dolomite in the SLZ and upper parts may be formed by organoclastic sulphate reduction, favouring precipitation by increased alkalinity. The AOM biomarkers in the SLZ include isoprenoid‐based archaeal membrane lipids, such as abundant glycerol dibiphytanyl glycerol tetraethers (GDGTs) dominated by GDGT‐2. The δ¹³C values of GDGT‐2, measured as ether‐cleaved monocyclic biphytanes, are as low as −100‰ versus V‐PDB. Further, bacterial dialkyl glycerol diethers with two anteiso‐C₁₅ alkyl chains and δ¹³C values of −81‰ are interpreted as biomarkers of sulphate‐reducing bacteria. The lipid biomarker signatures and mineralogical patterns suggest that anaerobic methane‐oxidizing archaea of the ANME‐1 group thrived in the subsurface at times of slow and diffusive methane seepage. Petrographic analyses revealed that the SLZ was exhumed at some point (e.g. signs of bioerosion of the semi‐lithified sediment), providing a hard substrate for CWC larval settlement. In addition, this work reveals that AOM‐induced semi‐lithification likely played a role in mound stabilization. Lipid biomarker analysis proves to be a powerful tool to disentangle early diagenetic processes induced by microbial metabolisms.

中文翻译：

---

通过脂质生物标记物限制在受渗流影响的冷水珊瑚丘中自生碳酸盐的形成。

冷水珊瑚（CWC）土丘是由珊瑚为主的层段与碳酸盐-硅质碎屑混合基质交替组成的。在某些地方，CWC土堆会受到甲烷渗流的影响，但人们对甲烷对CWC土堆的影响知之甚少。为了限制甲烷对CWC土堆生长的潜在影响，将脂质生物标志物研究与矿物学和岩石学分析相结合，以研究加的斯湾受渗水影响的CWC土堆中甲烷的厌氧氧化（AOM）和沉积物中自生的碳酸盐形成。 。在由自生文石，高镁方解石和钙过量白云石组成的半石化带（SLZ）中发现的特征性脂质证实了AOM的发生。高镁方解石的形成归因于AOM，它是一种石化剂。文石只是次要阶段。SLZ和上部中钙过量的白云石可能是通过有机碎屑硫酸盐的还原而形成的，有利于碱度的增加。SLZ中的AOM生物标志物包括基于类异戊二烯的古细菌膜脂质，例如以GDGT-2为主的丰富的甘油二双壬基甘油四醚（GDGT）。δGDGT-2的¹³ C值（以醚裂解的单环双环烷烃计）相对于V-PDB低至−100‰。此外，细菌二烷基甘油二醚具有两个反异-C _15支烷基链和δ ¹³C值-81‰被解释为硫酸盐还原菌的生物标记。脂质生物标志物的特征和矿物学特征表明，ANME-1组的厌氧甲烷氧化古细菌在甲烷扩散缓慢而扩散时在地下生长。岩石学分析表明，SLZ在某个时候被挖出（例如，半石化沉积物被生物侵蚀的迹象），为CWC幼虫的沉降提供了坚硬的基质。此外，这项工作表明，AOM引起的半石化可能在土丘稳定中起作用。脂质生物标志物分析被证明是解开由微生物代谢引起的早期成岩过程的有力工具。