Testing significance of total organic carbon isotope vlues for chronostratigraphy : Application to the Cretaceous Yezo Group in Hokkaido, Japan

To realistically interpret chronostratigraphic correlation based on carbon isotope stratigraphy, we clarified deviation of total organic δ¹³C values within a single sample, deviations of total organic δ¹³C values within identical horizons, and the relationship of δ¹³C values between total organic matter and wood fragments. The deviation (2σ ) of δ¹³C values of total oraganic matter (δ¹³Cᴛᴏᴍ values) within a single sample was 0.4‰. Maximum differences of δ¹³Cᴛᴏᴍ values from identical horizons were smaller than 0.4‰. Although cross-plots of δ¹³Cᴛᴏᴍ and δ¹³C values of wood fragments (δ¹³Cᴡᴏᴏd values) certify their proportional relationship, generally negative values of δ¹³Cᴛᴏᴍ relative to the δ¹³Cᴡᴏᴏd were also evident. Differences between δ¹³Cᴡᴏᴏd and δ¹³Cᴛᴏᴍ were between 0.2 and 1.9‰. Regarding this character of δ¹³Cᴛᴏᴍ distribution, its stratigraphic variations are applicable for stratigraphic and correlation purposes. This result provides important criteria for application of δ¹³C stratigraphy to the Yezo Group.