Discrimination of sediment provenance using rare earth elements in the Ulleung Basin, East/Japan Sea

Abstract

Abstract In order to discriminate the origins of Ulleung Basin (East/Japan Sea) sediments using rare earth elements (REEs), sediments from 15 box cores and one piston core collected in the shelf, slope, and basin were analyzed for major elements (Al, Fe, Ca, and Mn) and REEs. The major sedimentary components in this basin were presumed to be detrital materials from land, even in the basin sediments, based on Al and organic contents (carbon and opal). Post-depositional recycling processes involving Fe and Mn were identified in the basin sediments. Thus, the Ce anomaly and the fractionation factors of light REEs (LREEs) and middle REEs (MREEs) relative to heavy REEs (HREEs) could not be used as provenance indicators in the deep basin sediments (> 2000 m of water depth) based on a feasibility check using their covariation with Fe and Mn. For the shelf, slope, and basin B (sites near islands; water depths of 1200–1800 m) regions, the Eu anomaly, LREEN/HREEN, and MREEN/HREEN could be successfully used to discriminate possible provenances, including Nakdong River sediments (NRS), Chinese River sediments (CRS), Ulleungdo volcanic rocks (UVR), and Dokdo volcanic rocks (DVR). From the provenance indicators, slope as well as the shelf sediments (called the Korea Strait shelf mud; KSSM) in the Ulleung Basin can be regarded as mixtures of NRS and CRS with decreasing portions of NRS in the KSSM with distance from the Nakdong River. Basin B sediments were mixtures of UVR or DVR and CRS. These findings can be explained if sediments discharged from the Nakdong River were transported and deposited (KSSM) northward within the strong coastal front in normal periods and if sediment flumes from summer floods flowed out across the coastal front, were carried with the Tsushima Warm Current, and then deposited in the slope area. This study indicated that CRS were very important detrital sediments and that REE compositions can be successfully used as a provenance indicator in even hemipelagic sediments close to land.