Implications of seeping hydrocarbon gases in the Kunsan Basin, central Yellow Sea, off the southwest of Korea

Abstract

In the Kunsan Basin of the central Yellow Sea off the southwest Korea, a detailed analysis of high resolution (3.5 kHz) seismic profiles shows that hydrocarbon gases are actively seeping by forming numerous plumes. The uppermost sedimentary layer is acoustically masked, turbid or transparent with some acoustically enhanced internal reflectors, resulting from fully or partially charged gases. Sediment interstitial water methane is characterized by the enrichment of heavier carbon isotope (δ13C, -52.6~-44.7‰ PDB), indicating that the seeping gases are originated from deep structures and slightly degraded or mixed with newly formed biogenic ones during the migration rather than biological decomposition of organic matter at shallow depth of sediments. Gas seeping seems to have been strong as much as to erupt through a crater or raising a sedimentary dome by increased pressure of charged gases, although it is partially controlled by tidal cycle, not leaving pockmarks in the sandy seafloor.