Abstract

In this study, core sediments and pore water were analysed to identify the origin of organic matter and gas in late Quaternary sediments from the northwestern Ulleung Basin of the East Sea. C/N and C/S ratios in the sediments show that the organic matter in the study area originated predominantly from marine algae. However, the results of Rock-Eval pyrolysis indicate that the organic matter has an origin of the land-plant (Type III), locating in the immature stage. These different results might be due to the heavy oxidizing of the organic matter during sinking down to the seafloor or after deposition in the sediments. Concentration of sulfate in the pore water decreases gradually with core depth, while concentration of CH₄ increases gradually with core depth. This indicates that sulfate reduction and methanogenesis occurred actively in the sediments. Also, it is likely that the compositions of CH₄ are characterized as a more biogenic origin, mostly caused by microbial activity, rather than a thermogenic one.

Keywords core sediment, pore water, sulfate reduction, methanogenesis, late Quaternary, Ulleung Basin, East Sea