John Pohlman Jorn Peckmann Yuedong Sun Yu Hu Harry Roberts Duofu Chen Dong Feng 2021 <p><span>Sulfate-driven anaerobic oxidation of methane (AOM) limits the release of methane from&nbsp;marine sediments&nbsp;and promotes the formation of carbonates close to the seafloor in&nbsp;seepage&nbsp;areas along&nbsp;continental margins. It has been established that&nbsp;hydrocarbon seeps&nbsp;are a source of methane,&nbsp;dissolved inorganic carbon, and dissolved&nbsp;organic carbon&nbsp;to marine environments. However, questions remain about the contribution of deep-sourced carbon from hydrocarbon seeps to the sedimentary organic carbon pool. In this study, we analyzed carbon quantity, radiocarbon content (as percent modern carbon, pMC), stable carbon&nbsp;isotopic compositions&nbsp;(as δ</span>¹³<span>C) of organic matter enclosed within seep carbonates from the&nbsp;Gulf of Mexico&nbsp;and the South China Sea to assess if sediment organic matter may be used as a proxy for methane seepage intensity. The δ</span>¹³<span>C values of organic matter (δ</span>¹³<span>C</span>_org<span>) exhibited a large range from −81.4‰ to −23.9‰. Radiocarbon contents of the carbonate-bound organic matter in seep carbonates ranged from 6% to 28% pMC, suggesting organic matter of the carbonates is a mixture of marine&nbsp;particulate organic matter&nbsp;(δ</span>¹³<span>C&nbsp;=&nbsp;−22‰&nbsp;VPDB&nbsp;and 90% modern carbon) and biomass resulting from methane oxidation (assumed to have 0% modern carbon). Assuming constant productivity in the marine&nbsp;photic zone, it is proposed that seepage intensity and duration are the most important factors controlling the contribution of methane-derived carbon to the sedimentary column. This study reinforces the potential for using δ</span>¹³<span>C values of organic carbon to discern methane-rich environments in ancient&nbsp;sedimentary environments&nbsp;where authigenic carbonate is not present and to constrain the record of AOM through Earth history.</span></p> application/pdf 10.1016/j.chemgeo.2021.120572 en Elsevier Contribution of deep-sourced carbon from hydrocarbon seeps to sedimentary organic carbon: Evidence from radiocarbon and stable isotope geochemistry article