The fate of organic matter in deep-buried marine sediments determines the formation of hydrocarbon reservoirs, shapes the deep biosphere, and affects the global carbon cycle. Several geochemical processes such as silicate weathering, iron and manganese (hydr)oxide reduction, and sulfate reduction influence the remineralization of organic matter in buried sediments. However, little information on deep-seated organoclastic sulfate reduction is available and the involved geochemical processes are largely unknown. Here, authigenic carbonates recovered from Ship Shoal Block 296 (SS296) of the Gulf of Mexico, all dominated by low-magnesium calcite, were investigated to constrain organoclastic sulfate reduction in deep-buried sediments. The SS296 carbonates had been previously suggested to be of a deep origin and transported upward by salt diapirism. The presence of cone-in-cone textures in samples 3110R1 and 3110R2 as well as vitrinite reflectance values of 0.48% to 0.58% indicate carbonate formation at a relatively deep burial. Likewise, clumped isotope thermometry yielded formation temperatures from 45 °C to 53 °C for sample 3110R1, 60 °C for sample 3110R2, and 11 °C to 37 °C for sample 3110R3. In spite of formation at greater depth, the temperatures of samples 3110R1 and 3110R2 are still within the temperature range of microbial sulfate reduction, reflecting formation depths between 1 km and 2.7 km. The presence of framboidal pyrite and its relatively low δ³⁴S values (−27.8‰ to +11.5‰) agree with the occurrence of microbial sulfate reduction during carbonate precipitation. The carbon isotopic composition of the carbonates (δ¹³C: −16.6‰ to −8.9‰) and enclosed organic matter (δ¹³C_org: −26.8‰ to −20.5‰) suggests that organic matter is the dominant carbon source of carbonate minerals. This study confirms that microbial sulfate reduction occurs in deep-buried sediments, driving the degradation of organic matter. Our findings suggest that organoclastic sulfate reduction might be common in deep-seated sedimentary environments, controlling the fate of organic matter in deep subsurface environments and affecting the global carbon cycle.

深埋海洋沉积物中有机物的命运决定了油气藏的形成，塑造了深层生物圈，并影响了全球碳循环。几种地球化学过程，如硅酸盐风化、铁和锰（氢氧化物）氧化物还原以及硫酸盐还原影响埋藏沉积物中有机物的再矿化。然而，关于深层有机碎屑硫酸盐还原的信息很少，所涉及的地球化学过程在很大程度上是未知的。在这里，研究了从墨西哥湾船舶浅滩区块 296 (SS296) 中回收的所有以低镁方解石为主的自生碳酸盐，以抑制深埋沉积物中有机碎屑硫酸盐的还原。SS296 碳酸盐以前曾被认为具有深层起源并通过盐底辟向上输送。样品 3110R1 和 3110R2 中存在锥形纹理以及 0.48% 至 0.58% 的镜质体反射率值表明碳酸盐在相对较深的埋藏处形成。同样，聚集同位素测温法测得样品 3110R1 的地层温度为 45 °C 至 53 °C，样品 3110R2 为 60 °C，样品 3110R3 为 11 °C 至 37 °C。尽管地层深度较深，但样品 3110R1 和 3110R2 的温度仍在微生物硫酸盐还原的温度范围内，反映地层深度在 1 公里至 2.7 公里之间。柱状黄铁矿的存在及其相对较低的 δ 对于样品 3110R1，聚集同​​位素测温法得出的地层温度为 45 °C 至 53 °C，样品 3110R2 为 60 °C，样品 3110R3 为 11 °C 至 37 °C。尽管地层深度较深，但样品 3110R1 和 3110R2 的温度仍在微生物硫酸盐还原的温度范围内，反映地层深度在 1 公里至 2.7 公里之间。柱状黄铁矿的存在及其相对较低的 δ 对于样品 3110R1，聚集同​​位素测温法得出的地层温度为 45 °C 至 53 °C，样品 3110R2 为 60 °C，样品 3110R3 为 11 °C 至 37 °C。尽管地层深度较深，但样品 3110R1 和 3110R2 的温度仍在微生物硫酸盐还原的温度范围内，反映地层深度在 1 公里至 2.7 公里之间。柱状黄铁矿的存在及其相对较低的 δ³⁴ S值（-27.8‰至+11.5‰）与碳酸盐沉淀过程中微生物硫酸盐还原的发生一致。^{碳酸盐（δ 13} C：-16.6‰至-8.9‰）和封闭有机质（δ ¹³ C _org ：-26.8‰至-20.5‰）的碳同位素组成表明有机质是碳酸盐矿物的主要碳源. 该研究证实，微生物硫酸盐还原发生在深埋沉积物中，推动了有机物的降解。我们的研究结果表明，有机碎屑硫酸盐还原可能在深层沉积环境中很常见，控制着深层地下环境中有机物的命运并影响全球碳循环。