Abstract

Although siliceous sediments have the potential to reveal an enigmatic Miocene climate evolution, problems with age model construction are tough to beat. Cyclostratigraphy is a useful tool for the construction of a high-resolution age model. In the Japan Sea region, orbital-scale oscillations in the sedimentary environment of the Miocene sedimentary basins are reported, for example, the Onnagawa Formation in Akita Prefecture in northern Japan and the Nakayama Formation on Sado Island in central Japan. In this study, we constructed a high-resolution age model of the Miocene siliceous sediment in the Japan Sea, the Nakayama Formation, by cyclostratigraphy using the geochemical properties of the sediment. Ratios of the biogenic silica content to the detritus content in the sediment were determined based on the X-ray fluorescence (XRF) and X-ray diffraction (XRD) measurements. Orbital-scale oscillations were identified in the ratios of biogenic silica to detritus, and it was used for cyclostratigraphic correlation with the global oxygen stable isotope (δ18O) curve of benthic foraminifera. Our new cyclostratigraphic age model and method are expected to promote using the Miocene siliceous sediments for paleoceanographic and paleoclimatologic studies. Additionally, major element and mineral compositions determined by XRF and XRD analysis were used to reconstruct the sedimentary environment on which the East Asian Monsoon system may have an influence.