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

Long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record. Alkenone and n-alkane biomarker measurements in an exceptionally continuous and well constrained sedimentary succession in Japan can be used to reconstruct ocean and atmospheric changes throughout the Pleistocene.

Automated summary

Using long-chain alkenones and n-alkanes to reconstruct past environments is common, but applying this technique to exposed sedimentary rock sequences can be challenging due to potential alterations. A study in Japan's Kazusa Group found that the biomarkers preserved there could provide a detailed record of Pleistocene paleoenvironments, specifically reflecting changes in sea surface temperature and terrestrial climate. This suggests that the biomarker measurements in the Kazusa Group could help reconstruct ocean and atmospheric changes throughout the Pleistocene.