Carbon isotope compositions of sedimentary organic matter (average −24.1‰) from an Albian marine siliciclastic succession in Hokkaido, Japan, exhibit a distinct anomaly by ∼+1.2‰ with a trifurcate shape across the Albian–Cenomanian boundary and two relatively small shifts (<+1‰) in the middle and upper Albian, respectively. The organic matter consist predominantly of woody materials with an insignificant degree of thermal alteration, judged from the visual and elemental characteristics of kerogen; the stratigraphic δ13Corg fluctuations are independent of lithological or total organic carbon variations. Thus, the Hokkaido δ13Corg profile is interpreted as representing the temporal δ13C changes in whole C3 plant vegetation in the provenance of East Asia during Albian time. The patterns and amplitudes in δ13Cwood values and their relationship with planktonic foraminiferal zones are conformable with coeval Tethyan δ13C records of pelagic carbonates. This observation reinforces the view that δ13C compositions of marine and terrestrial carbon reservoirs fluctuated simultaneously by the same amplitude within the ocean-atmosphere-biosphere system regardless of changes in such paleoenvironmental parameters as pCO2. From a chemostratigraphic viewpoint, time-equivalent levels of Oceanic Anoxic Events and stage boundaries are constrained for the Hokkaido sections, allowing for the proposal of a detailed chronostratigraphic framework for future advanced paleoceanographic research in the mid-Cretaceous northwestern Pacific region.