VARIATIONS OF TERRIGENOUS SEDIMENT SUPPLY TO THE SOUTHERN SLOPE OF THE ULLEUNG BASIN, EAST/JAPAN SEA SINCE THE LAST GLACIAL MAXIMUM

Abstract

In order to examine the variations of terrigenous detrital components in the core (97PC-19) sediments from the southern margin of the Ulleung Basin, we detail changes in grainsize composition and contents of major elements such as detrital SiO2 (detSiO2), TiO2, Al2O3, MgO and K2O since the Last Glacial Maximum (LGM). The variations of detrital components are characterized by the significant elevations of detSiO2/Al2O3 and TiO2/Al2O3 ratios with the concomitant increase of silt to clay ratios during the last deglaciation (10–15 ka). Such a prominent increase suggests an enhanced flux of detrital quartz and Ti-bearing minerals relative to Al-rich clay minerals which can be attributed to either aeolian transport or hemipelagic advection. Similar variations of detrital components during the last deglaciation are much more pronounced in the core 95PC-1, located more proximal to the Korea Strait, as evidenced by the high sedimentation rate and sand and silt contents. However, this temporal variation is not clearly observed in ODP site 797 far from the Korea Strait. The spatial change of the detrital components among the cores suggests a primary control of hemipelagic fluxes of riverine sediments relative to aeolian dust fluxes on the variations of detrital components since the LGM. The hemipelagic fluxes were most likely derived from the paleochannels of the Nakdong River that extended onto the shelf margin of the Korea Strait during the last sea-level lowstand and increased by shore-parallel transport of paleocurrents through the Korea Strait during the early stage of the postglacial transgression.