Carbon isotope fluctuations of sedimentary organic matter along the two geological traverses in the Yezo Group, Hokkaido, northern Japan, elucidate a detailed chemostratigraphy for the Cenomanian Stage on the northwestern Pacific margin. Visual characterization of the kerogen from mudstone samples shows that the major constituents of sedimentary organic matter originated as terrestrial higher plants. The atomic hydrogen/carbon ratios of the kerogen suggest that the original d 13 C values of terrestrial organic matter (TOM) have not been affected significantly by thermal diagenesis. The patterns in two d 13 C TOM curves are similar and independent of changes in lithology and total organic carbon contents, which suggests that TOM was mixed sufficiently before the deposition in the Yezo forearc basin for the d 13 C composition having been homogenized. In addition, this implies that the Hokkaido d 13 C TOM profiles represent the averaged temporal d 13 C variations of terrestrial higher-plant vegetation in the hinterlands of northeast Asia during Cenomanian time. Three shorter-term (ca. 0.1 my duration) positive-and-negative d 13 C TOM fluctuations of~1‰ are present in the Lower to Middle Cenomanian interval in the Yezo Group. On the basis of the age-diagnostic taxa (ammonoids, inoceramids and planktic foraminifers), these discrete d 13 C TOM events are interpreted to be correlated with those in the d 13 C curves of pelagic carbonates from European basins. The correlation of d 13 C events between the European and Yezo Group sections suggests that the shorter-term d 13 C fluctuations in Cenomanian ocean-atmosphere carbon reservoirs are useful for global chemostratigraphic correlation of marine strata. In particular, the correlation of d 13 C fluctuations of the so-called 'Mid-Cenomanian event' (MCE) implies: (i) the d 13 C variations of global carbon reservoir during the MCE are precisely recorded in the d 13 C TOM records; and (ii) the MCE d 13 C TOM event is an efficient chronostratigraphic index for the Lower/ Middle Cenomanian boundary of the Mid-Cretaceous sequences.