Molecular fossils reveal fluid composition and flow intensity at a Cretaceous seep

摘要: An isolated Hauterivian marine limestone from the Crimean Peninsula containing masses of articulated specimens dimerelloid brachiopod Peregrinella has previously been interpreted to represent a hydrocarbon-seep deposit. In order constrain intensity seepage and composition fl uids, we investigated lipid biomarker inventory this seep limestone. The dominant biomarkers are (13)C-depleted isoprenoids including tail-to-tail linked pentamethylicosane (delta(13)C value: -108 parts per thousand), representing molecular fossils methanotrophic archaea. This observation reveals that uids contained methane. Because carbonates have found be only moderately values as low -14 signifi cant contribution less carbon source than methane, probably carbonate, is apparent. Such degree admixture carbonate typical for limestones resulting ow rates. observed pattern with prominent occurrence biphytanes, but lacking crocetane, archaea at site were similar ANME-1 cluster. Archaea cluster known able cope lower methane concentrations ANME-2 archaea; therefore better adapted rates diffusive ow. contains small amount early diagenetic cement. Based on comparison patterns other ancient deposits, it apparent typically results in little cement, whereas advective, more intense appears favor cement precipitation. If applied caution, supposed relationship can used fi rst approximation intensity.