Evaluation of paleoenvironment using terpenoid biomarkers in lignites and plant fossil from the Miocene Tokiguchi Porcelain Clay Formation at the Onada mine, Tajimi, central Japan

► We analyze terpenoid in sediments of Miocene lignite and clay beds, and plant fossil. ► Coniferous diterpenoid is mainly detected in sediments in the lignite and clay beds. ► Low hopane isomer ratio and biosterol detection show the lignite seams are immature. ► Lower stanol/sterol ratios of lignite seams are due to microbial reduction in swamp. ► Angiosperm-derived triterpenoids are detected as contaminant in a conifer fossil.