Integrated stratigraphy of the Lower Cretaceous (Berriasian–Valanginian–Hauterivian) successions in Northwest Panthalassa, Northeast Japan

The Valanginian Stage is characterized by the first major perturbation of the global carbon cycle in the Cretaceous and the initial emplacement of large igneous provinces. With the ratification of the global boundary stratotype sections and points (GSSPs) for the base of Valanginian and Hauterivian stages has come increased stratigraphic and palaeoenvironmental research on the Valanginian. However, paleoceanographic information remains limited for the Early Cretaceous Panthalassa, which was the largest ocean during this period. In Northeast Japan, Lower Cretaceous marine successions, formed in the northwestern region of Panthalassa along the northeastern margin of Eurasia, are sporadically exposed. These successions have been challenging to date accurately due to the limited availability of age-diagnostic fossils. We establish new global stratigraphic correlations using laser ablation U–Pb zircon ages from tuffs and carbon isotope stratigraphy for the Lower Cretaceous formations of the Karakuwa and Oshima Groups in Northeast Japan. We identify the Weissert Event within these strata, and identify potential stratigraphic levels for the Berriasian/Valanginian and Valanginian/Hauterivian boundaries. Notably, the Weissert Event interval within these successions exhibit no evidence for a decrease in bottom-water dissolved oxygen, such as the intercalation of black shales or a decrease in bioturbation observed elsewhere. On the other hand, observed lithological change of the studied successions is indicative of eustatic sea-level changes or regional tectonics, including large-scale sinistral strike-slip movement and subsequent ridge subduction along the active continental margin of Eurasia. • Approximate horizons of the Berriasian/Valanginian and Valanginian/Hauterivian boundaries and Weissert Event were identified in the Lower Cretaceous marine sequences of Northwest Panthalassa based on macrofossils, δ 13 C stratigraphy, and U–Pb ages of tuffs. • The Weissert Event interval in the Lower Cretaceous of Northwest Panthalassa does not show significant lithological changes, such as the intercalation of black shales and/or a decrease in bioturbation.