Mineralogy, geochemistry, and sources of clay minerals in sediments of the Ulleung Basin, East Sea (Sea of Japan)

The provenance of sediments in the Ulleung Basin, East Sea (Sea of Japan), could be attributed to diverse sources, including the Tsushima Warm Current (TWC) and Korean coast. However, the contributions of these sources and their impacts on the composition of clay minerals, the distribution and composition of which can be used to decipher the paleoenvironment and provenance of sediments, remain obscure. Therefore, herein, we aimed to characterize the paleoenvironments and provenance of the sediments from the Ulleung Basin by analyzing their clay mineral compositions using X-ray diffraction and transmission electron microscopy-energy dispersive X-ray spectroscopy. For analysis, sediment cores were obtained during an expedition from March 30 to April 10, 2021, aboard the Onnuri R/V, and these were assigned three provenances: Korean coast, TWC, and a mixture of both. Results showed that clay minerals are abundant in the surface sediments and are dominated by illite (mean = 49.1%). Clay mineral composition changes in a southwest to northeast direction. Sediments sourced from the TWC are poor in smectite and rich in illite. In contrast those assigned a mixed provenance are rich in illite and poor in kaolinite and chlorite. This change is particularly evident toward the Dokdo area (from SW to NE). Moreover, piston core samples from St. 8 and 10 also indicate the presence of plagioclase, microcline, and quartz. We found a rhodochrosite layer in St. 8 samples, at a depth of 3.96 and 4.00 m, which represents the transition from the Last Glacial Maximum (LGM) to the Holocene. Our results indicated that the input of smectite in the basin increased from the LGM to the present whereas that of other clay minerals decreased. The smectite originated mainly from the Korean coast and illite from the TWC. Kaolinite and chlorite in the sediments exhibited similar horizontal and vertical patterns, which are attributed to the interaction between climate, ocean currents, and sediment sources. Moreover, Al- and Fe-rich smectites were observed, compositional variations of which could be attributed to source differences. These results are indicative of other sources of smectites in addition to the three provenances highlighted. This study provides a detailed analysis of sediment sources and horizontal and vertical clay mineral composition changes and shows the difference between them. Sediment from the Ulleung Basin was affected by not only aeolian dust but other factors, such as various sediment sources, ocean circulation, and climate change.