An organic geochemical study of KP-2 core on the mud volcano at Nankai Trough

Organic geochemical data was collected from a KP-2 piston core sample obtained from a mud volcano in the Nankai Trough, off the southeast coast of Japan. The Nankai Trough was investigated geologically and was found to have a large amount of methane hydrates. Biomarkers indicating anaerobic oxidation of methane (AOM) were expected to be found in the sediment of the mud volcano collected by KP-2 core. But the gas chromatography-mass spectrometry (GC-MS) analysis of the samples showed only one biomarker related to the methane-oxidizing Archaea, namely 2,6,10,15,19-pentamethyleicosane (PME), could be detected throughout the KP-2 core. Phytane was predominant in the upper part of the KP-2 core; however, a series of 2,2-dimethylalkanes (2,2-DMAs) were characterized in the lower part of KP-2 core. The individual δ13C values of 2,2-DMAs, which were − 29.1 to − 27.3‰ indicate that the origin of 2,2-DMAs was not related to methane-oxidizing Archaea.