REE geochemistry and paleoenvironmental characteristics in the Ulleung Basin, East Sea (Sea of Japan), over the past 120 kyr BP

Abstract

Paleoenvironments of the East Sea are influenced by global sea level changes and sea ice expansion during the Quaternary, and evidence of anoxic bottom water conditions and frequent changes in the properties of inflowing surface water have been presented due to the shallow entrances. In order to understand the paleoenvironmental characteristics of the Ulleung Basin, rare earth elements (REEs) geochemistry was investigated during oxygen isotope stages 1-5. Among the REEs, it was revealed that the diagenetic MREEs (Sm, Eu, Gd, Tb, Dy) enrichments compared to other REEs could be used as the indices to interpret the sedimentary environment. In this study, therefore, the UCC (upper continental crust)-normalized ratios of LREEs (La, Pr, Nd) to HREEs (Ho, Tm, Yb, Lu) were used to identify the riverine sediments, indicating the predominant Chinese river sediments, but the Korean river sediments mixed during the stages 2 and 5.4. In addition, the positive Ce and Eu anomalies were found after ca. 100 kyr BP with sea level decrease gradually. Especially, the strong positive Eu anomaly (max ca. 10) was found at stage 2. The vertical profile of Eu anomaly was consistent with that of Sr/Ca ratios, which showed a mirror image against the Sr/Al ratios, indicating exchange of Eu2+ and Sr2+ in reducing conditions. Consequently, the variations of REEs fractionations after ca. 100 kyr BP are likely associated with the fluctuation of thebeen presented due to the shallow entrances. In order to understand the paleoenvironmental characteristics of the Ulleung Basin, rare earth elements (REEs) geochemistry was investigated during oxygen isotope stages 1-5. Among the REEs, it was revealed that the diagenetic MREEs (Sm, Eu, Gd, Tb, Dy) enrichments compared to other REEs could be used as the indices to interpret the sedimentary environment. In this study, therefore, the UCC (upper continental crust)-normalized ratios of LREEs (La, Pr, Nd) to HREEs (Ho, Tm, Yb, Lu) were used to identify the riverine sediments, indicating the predominant Chinese river sediments, but the Korean river sediments mixed during the stages 2 and 5.4. In addition, the positive Ce and Eu anomalies were found after ca. 100 kyr BP with sea level decrease gradually. Especially, the strong positive Eu anomaly (max ca. 10) was found at stage 2. The vertical profile of Eu anomaly was consistent with that of Sr/Ca ratios, which showed a mirror image against the Sr/Al ratios, indicating exchange of Eu2+ and Sr2+ in reducing conditions. Consequently, the variations of REEs fractionations after ca. 100 kyr BP are likely associated with the fluctuation of the