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A group of 2,6,10,15,19-pentamethyli- cosenes (PMIΔ) containing 1―5 unsaturated double bonds has been identified in the sea floor sediments from the Gulf of Mexico at the Green Canyon 238 site.These PMIΔ compounds are distributed between nC22 and nC24 on the mass chromatogram of aliphatic fraction. Their δ 13C values are very much depleted in 13C and in the range of ?86.7‰ to ?115.5‰, whereas the δ 13C values of companion n-alkanes range from ?28.4‰ to ?34.6‰. These unsaturated PMIΔ com-pounds are typical biomarkers derived from the an-aerobic oxidation of methane mediated by meth-ane-oxidizing archaeal bacteria and indicative of the gas seeps or even the occurrence of gas hydrates in the deep sea sediments.
A group of 2,6,10,15,19-pentamethyl-cosenes (PMIΔ) containing 1-5 unsaturated double bonds has been identified in the sea floor sediments from the Gulf of Mexico at the Green Canyon 238 site. The PMI Δs are are distributed between nC22 and nC24 on the mass chromatogram of the aliphatic fraction. Their δ 13C values are very much depleted in 13C and in the range of? 86.7 ‰ to 115.5 ‰, while the δ 13C values of companion n-alkanes range from? 28.4 ‰ to 34.6 ‰. These unsaturated PMIΔcom-pounds are typical biomarkers derived from the an-aerobic oxidation of methane mediated by meth-ane-oxidizing archaeal bacteria and indicative of the gas seeps or even the occurrence of gas hydrates in the deep sea sediments.