• journal_title：Geosphere
• Contributor：Go-Ichiro Uramoto ; Rui Tahara ; Toru Sekiya ; Hiromichi Hirano
• Publisher：Geological Society of America
• Date：2013-04-01
• Format：text/html
• Language：en
• Identifier：10.1130/GES00835.1
• journal_abbrev：Geosphere
• issn：1553-040X
• volume：9
• issue：2
• firstpage：355
• section：CURRENT ISSUE ARTICLES

Carbon isotope data of terrestrial organic matter (δ¹³C_TOM) obtained in Hokkaido, northern Japan, from the marine Cretaceous Yezo Group along the northwestern Pacific 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 fluctuations in these events show similar patterns in the Yezo Group, indicating that terrestrial organic matter is mixed sufficiently 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 chemostratigraphic 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 identifies changes in isotopic difference between δ¹³C_TOM and δ¹³C_carbonate (Δ_{TOM–carbonate}), which are interpreted to reflect 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 lowering of atmospheric pCO₂ or decrease of climate stress related to the diverse paleoclimatic cooling is interpreted to have restored the ocean-atmosphere δ¹³C trends.