Abstract Numerous marine hydrocarbon seeps have been discovered in the past three decades, the majority of which are dominated by methane-rich fluids. However, an increasing number of modern oil seeps and a few ancient oil-seep deposits have been recognized in recent years. Oil seepage exerts significant control on the composition of the seep-dwelling fauna and may have impacted the marine carbon cycle through geological time to a greater extent than previously recognized. Yet, distinguishing oil-seep from methane-seep deposits is difficult in cases where δ13Ccarb values are higher than approximately −30‰ due to mixing of different carbon sources. Here, we present a comparative study of authigenic carbonates from oil-dominated (site GC232) and methane-dominated (site GC852) seep environments of the northern Gulf of Mexico, aiming to determine the geochemical characteristics of the two types of seep carbonates. We analyzed (1) major and trace element compositions of carbonates, (2) total organic carbon (TOC), total nitrogen (TN) and carbon isotope (δ13CTOC) of residue after decalcification, (3) sulfur isotope signatures of chromium reducible sulfur (CRS, δ34SCRS) and residue after CRS extraction (δ34STOS), as well as (4) sulfur contents (TOS) of residue after CRS extraction. Carbonates from the studied oil seep are dominated by aragonite and exhibit lower δ34SCRS values, suggesting carbonate precipitation close to the sediment surface. In addition, oil-seep carbonates are characterized by higher TOC and TOS contents and higher TOC/TN ratios, as well as less negative δ13CTOC values compared to methane-seep carbonates, probably reflecting a contribution of residual crude oil enclosed in oil-seep carbonates. Very low δ13CTOC values (as low as −68.7‰, VPDB) and low TOC/TN ratios of methane-seep carbonates indicate that the enclosed organic matter is derived mainly from the biomass of methanotrophic biota. This study presents new geochemical data that will allow the discrimination of oil-seep from methane-seep deposits. Although some of the geochemical patterns are likely to be affected by late diagenesis, if applied with caution, such patterns can be used to discern the two end-member types of seepage – oil seeps and methane seeps – in the geological record.

中文翻译：

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一种识别海洋渗漏处形成的自生碳酸盐的碳氢化合物来源（石油与甲烷）的新方法

摘要 在过去的 30 年里，已经发现了大量的海洋油气渗漏，其中大部分以富含甲烷的流体为主。然而，近年来已发现越来越多的现代石油渗漏和一些古老的石油渗漏沉积物。石油渗漏对栖息于渗漏的动物群的组成具有显着的控制作用，并且可能在地质时期对海洋碳循环的影响比以前认识到的更大。然而，由于不同碳源的混合，在δ13Ccarb 值高于大约-30‰的情况下，很难区分油渗出物和甲烷渗出物沉积物。在这里，我们对墨西哥湾北部以石油为主（地点 GC232）和以甲烷为主（地点 GC852）渗漏环境的自生碳酸盐进行了比较研究，旨在确定两类渗流碳酸盐的地球化学特征。我们分析了（1）碳酸盐的主要和微量元素组成，（2）脱钙后残留物的总有机碳（TOC）、总氮（TN）和碳同位素（δ13CTOC），（3）铬可还原硫的硫同位素特征（ CRS, δ34SCRS) 和 CRS 萃取后的残渣 (δ34STOS)，以及 (4) CRS 萃取后残渣的硫含量 (TOS)。来自研究的石油渗漏的碳酸盐以文石为主，并表现出较低的 δ34SCRS 值，表明碳酸盐沉淀靠近沉积物表面。此外，与甲烷渗出碳酸盐相比，渗油碳酸盐具有更高的 TOC 和 TOS 含量和更高的 TOC/TN 比，以及更小的负 δ13CTOC 值，可能反映了包含在渗油碳酸盐中的残余原油的贡献。非常低的 δ13CTOC 值（低至 -68.7‰，VPDB）和甲烷渗出碳酸盐的低 TOC/TN 比率表明封闭的有机物质主要来自甲烷营养生物群的生物量。这项研究提供了新的地球化学数据，可以区分石油渗漏和甲烷渗漏沉积物。虽然一些地球化学模式可能会受到晚期成岩作用的影响，但如果谨慎应用，这些模式可用于识别地质记录中两种端元类型的渗漏——石油渗漏和甲烷渗漏。VPDB) 和甲烷渗出碳酸盐的低 TOC/TN 比率表明封闭的有机物质主要来自甲烷营养生物群的生物量。这项研究提供了新的地球化学数据，可以区分石油渗漏和甲烷渗漏沉积物。虽然一些地球化学模式可能会受到晚期成岩作用的影响，但如果谨慎应用，这些模式可用于识别地质记录中两种端元类型的渗漏——石油渗漏和甲烷渗漏。VPDB) 和甲烷渗出碳酸盐的低 TOC/TN 比率表明封闭的有机物质主要来自甲烷营养生物群的生物量。这项研究提供了新的地球化学数据，可以区分石油渗漏和甲烷渗漏沉积物。虽然一些地球化学模式可能会受到晚期成岩作用的影响，但如果谨慎应用，这些模式可用于识别地质记录中两种端元类型的渗漏——石油渗漏和甲烷渗漏。