Upper Cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from Sakhalin, Russian Far East: a proxy for the isotopic composition of paleoatmospheric CO2

Time-stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from Cenomanian–Maastrichtian successions for the Russian Far East can be correlated to those of carbonate carbon from well-studied successions for other parts of the world. Age-indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in Japan and can be applied to the whole Cretaceous succession except for the Upper Cenomanian–Lower Turonian and the upper part of the Maastrichtian (zones lacking macrofossils). Globally correlative carbon isotopic events previously documented with carbonate carbon from Europe and with carbonate carbon and marine organic matter from the U.S. Western Interior are recognized with similar magnitude through uppermost Cenomanian–Lower Campanian. In ascending order these events are: positive ‘spike’ across the Cenomanian–Turonian boundary; step-like leveled segment followed by negative shift (Lower–Middle Turonian); trough-like negative excursion (Middle–Upper Turonian); positive rebound coupled with following broad peak (Coniacian); and positive peak (basal Campanian) followed by modest negative excursion. The parallel fluctuation of the δ13C value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric CO2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of CO2 in the ocean–atmosphere system. In the Upper Campanian and Maastrichtian, a negative δ13C excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from South and North Atlantic, the Indian, and the Pacific Oceans. Within this interval, the δ13C value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global CO2 reservoir with relatively minor regional/local ‘noise’.