Biomarkers in the rock outcrop of the Kazusa Group reveal paleoenvironments of the Kuroshio region

The classical biomarkers of long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct paleoenvironments. Here, we detected these biomarkers are preserved in the rock outcrop of the Kazusa Group exposed in central Japan, the most continuous sedimentary succession in the world, covering almost the entire Pleistocene. The alkenone unsaturation ratio and average chain length of n-alkanes appeared to reflect the glacial-interglacial changes in the sea surface temperature (SST) and terrestrial climate, respectively. Alkenone-based SSTs during 1.1–1.0 Ma were significantly higher than present-day SSTs in the same area, as supported by foraminiferal Mg/Ca-based temperatures, possibly reflecting the direct intrusion of the warm Kuroshio Current. Applying these biomarkers, which might be circumstantially preserved owing to their immunity to high temperature and consolidation stress during burial and uplift, we expect that the Kazusa Group should reveal detailed oceanic and atmospheric changes of the Kuroshio region.