Provenance study of the Miocene hemipelagic sediments in the Shikoku Basin and implication for the earlier history of the Kuroshio Current

Abstract

The Kuroshio Current (KC) is the biggest western boundary current in the northwest Pacific Ocean and plays an essential role in the Cenozoic climate evolution and ocean circulation changes. Paleoceanography of the Shikoku Basin, located downstream of the KC region, is sensitive to the evolution of the KC. In this study, the Miocene hemipelagic sediment supply in the Shikoku Basin has been investigated on sediments from lithologic Unit III of IODP Site C0011 using a combination of rock magnetism, Sr isotope composition, grain size analysis, and calcareous nannofossil study. Integrated results reveal that multidomain (MD) (titano-) magnetite concentration increases in the upper part of Unit III since ~10–11 Ma with elevated 87Sr/86Sr values (0.712–0.714) and fining up sediment grain size. Magnetic parameters, Sr isotope composition, and grain size, as reliable indicators of sediment sources, have been used to discriminate the geological sources of the sediments and attribute the increase in MD (titano-) magnetite concentration to the increasing detrital input from the East China Sea (ECS), which is rich in fine-grained particles and coarse-grained magnetite and have high 87Sr/86Sr ratio (0.712–0.727). Furthermore, the intensified western boundary current later became known as the KC is interpreted as a plausible reason for increasing fine-grained flux from the ECS. Our study provides a much earlier record of the KC at ~10–11 Ma, giving new insight into understanding the Cenozoic ocean circulation changes and climate evolution in the northwest Pacific Ocean.