Carbon isotope stratigraphy of terrestrial organic matter for the turonian (upper cretaceous) in northern Japan: Implications for oceanatmosphere δ¹³C trends during the mid-cretaceous climatic optimum

Carbon isotope data of terrestrial organic matter (δ¹³C_TOM) obtained in Hokkaido, northern Japan, from the marine Cretaceous Yezo Group along the northwestern Pacifi c margin elucidated a detailed chemostratigraphy for the Turonian Stage in this region of East Asia. Chemostratigraphic intra-basin correlation reveals three positive δ¹³C_TOM events in the Middle-Upper Turonian of the Yezo Group. δ¹³C_TOM fl uctuations in these events show similar patterns in the Yezo Group, indicating that terrestrial organic matter is mixed suffi ciently before deposition in the Yezo Basin. These δ¹³C_TOM events are correlated with previously documented δ¹³C_carbonate events in Europe (the Lulworth-Round Down, Glynde-Pewsey, and Late Turonian Events) based on global biostratigraphy. Our chemostrati graphic correlations strengthen the use of these δ¹³C events for global correlation of the Turonian marine successions. In addition, global correlation of Turonian marine and terrestrial δ¹³C events identifi es changes in isotopic difference between δ¹³C_TOM and δ¹³C_carbonate (Δ_{TOM-carbonate}), which are interpreted to refl ect changes in atmospheric pCO₂ levels, and climate-driven stresses of humidity and soil processes. In earlier stages of Turonian, Δ_{TOM-carbonate} values are increased. Elevated atmospheric pCO₂, and increased humidity and soil processes in enhanced greenhouse conditions during mid-Turonian, are interpreted to enlarge Δ_{TOM-carbonate} values. In later stages of Turonian, Δ_{TOM-carbonate} values are at a constant level, and the loweringof atmospheric pCO₂ or decrease of climate stress related to the diverse paleoclimatic cooling is interpreted to have restored the ocean-atmosphere δ¹³C trends.