Upper Cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from Sakhalin, Russian Far East: a proxy for the isotopic composition of paleoatmospheric CO2 by T. Hasegawa et al.—Discussion

Abstract

[Hasegawa, T., Pratt, L.M., Maeda, H., Shigeta, Y., Okamoto, T., Kase, T., Uemura, K., 2003. Upper Cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from Sakhalin, Russian Far East: a proxy for the isotopic composition of paleoatmospheric CO 2 . Palaeogeogr. Palaeoclimatol. Palaeocol. 189, 97–115] present highly interesting patterns in stable carbon isotopic ratios based on terrestrial organic matter from Cenomanian—Maastrichtian successions in Sakhalin Island and try to match these with carbonate carbon curves from other parts of the world. Although we agree that this approach is useful and do not doubt their methods or isotopic fluctuation results, we worry about the lack of any detailed stratigraphic scheme in the paper. Our main arguments: (1) Hasegawa et al. do not show Cenomanian/Turonian stage boundary positions in the Naiba section precisely, and, as a result, it seems that the positive spike shown at this boundary might not equate with this level but relate to the upper of two Cenomanian spikes established in Japan; (2) the definition of Turonian/Coniacian boundary is also imprecise and it is difficult to understand at what level in the Naiba section they place this boundary. As a result, it seems that the positive spike which has been shown near the middle of the Coniacian could correspond to the T—C boundary; (3) the imprecise interpretation of the Campanian/Maastrichtian boundary also causes the assumption that the negative spike, which Hasegawa et al. equate with the C—M boundary could be correspond to middle of upper Maastrichtian in the Naiba section.