Constraining the depositional age of an Upper Cretaceous non-marine and shallow marine siliciclastic succession, Kuji Group, northeastern Japan, based on carbon isotope stratigraphy and U−Pb radiometric dating

Determining detailed geologic ages for pre-Quaternary non-marine and shallow marine siliciclastic successions has generally been difficult due to the rare occurrence of age-diagnostic fossils. In this study, we present the first record of stable carbon isotope stratigraphy derived from detrital woods with U-Pb radiometric dating for felsic tuffs in the Upper Cretaceous Kuji Group, northeast Japan, for which the geologic age has been poorly constrained to date. The radiometric ages for each tuff, obtained by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analyses, range from 92.6 ± 0.6 to 79.1 ± 1.2 Ma (95% confidence interval). The composite δ13Cwood curve in the Kuji Group is correlated to the Upper Cretaceous reference sections in the Northwest Pacific, North America and Northwest Europe. Based on our correlations, several global carbon isotope excursion events in the late Turonian-early Campanian interval were recognized, and the Upper Cretaceous stage boundaries in the Kuji Group were partially identified, which agree well with previous biostratigraphic assumptions. Further, the depositional age of the dinosaur-bearing bone bed in the Kuji Group was estimated to be restricted to the early-middle Santonian. Our detailed chronostratigraphic framework provides significant implications for sequence stratigraphy, regional tectonic reconstruction and further exploration into the terrestrial ecosystem of the Late Cretaceous East Asian continental margin.