Sedimentation and seafloor mound formation in the southern slope of the Ulleung Basin, East Sea, Korea, since the Last Glacial Maximum

摘要

Detailed analysis of core sediments and acoustic characteristics of Chirp sub-bottom profiles from a submarine ridge in the southern slope of the Ulleung Basin, East Sea, Korea, reveals changes in sedimentary processes and deformation of sedimentary sequence induced by seafloor mound formation since the Last Glacial Maximum (LGM). The core sediments consist generally of four sedimentary facies which represent hemipelagic sedimentation under a poorly-oxygenated bottom-water condition during the LGM (crudely laminated mud), shoreface erosion and seaward transport off the shelf break during the post-glacial transgression (bioturbated sandy mud or muddy sand), hemipelagic sedimentation under generally well-oxygenated bottom-water condition after the sea-level rise (bioturbated mud), and episodic precipitation of authigenic carbonates by methane venting since the LGM (authigenic carbonate-bearing mud), respectively. The formation of authigenic carbonate-bearing mud facies and associated accumulation of near-seafloor gas hydrates might have led to up-warping of the sediment cover since the LGM that resulted in the seafloor mounds protruding along the crest line of the ridge. The effects of up-warping by expansion of the subsurface gas hydrates are firstly manifested in this paper by the abrupt lateral changes in the sedimentary facies distribution and uplifted acoustic reflectors between the mounds and the background seafloor.