The Stratigraphy and Paleontology of the Tetori Group in Central Japan Probably Contribute to the Marine and Non-Marine Stratigraphic Correlation in East Asia and Marine Paleobiogeographic Reconstruction in the Mid-Latitudes of the Northwest Pacific in the Early Cretaceous

The Tetori Group is the latest Jurassic to Early Cretaceous siliciclastic stratum sporadically distributed in northern Central Japan. Its lower part is mainly composed of shallow marine to brackish deposits, and its upper part fluvial to terrestrial ones. Thus, this group deposited in the transitional area between marine and non-marine environments, providing the clues to correlate the non-marine strata in the Korean Peninsula and China with the marine strata in the Pacific side of Japan. Furthermore, since it deposited on the North China Block or Central Asian Orogenic Belt in the eastern margin of the already amalgamated Asian Continent, its marine biota represents the one flourishing in the mid-latitudes of the Northwest Pacific at that time. Ammonoids from the Tetori Group indicates the marine strata are the Tithonian, Berriasian and Hauterivian ages. Endemic inoceramid species are also recovered from these strata. No buchiid record has been known from this group, contrary to coeval deposits in the Far-east Russia, Northeast China and also northern California, though boreal belemnites, which was described from northern California and Siberia, occur in the Berriasian Mitarai Formation of the Tetori Group. Recently, carbon isotope stratigraphy and zircon U-Pb dating were applied to the Tetori Group, and the horizons correlated with the Hauterivian long-term negative excursion and the positive excursion associated with OAE1a in the Aptian were recognized. Furthermore, the Volgian Isotopic Carbon Excursion (VOICE) is potentially recorded in the lowermost part of the Tetori Group. Further studies of the stratigraphy and paleontology of the Tetori Group probably contribute to the marine and non-marine stratigraphic correlation in East Asia and also marine paleobiogeographic reconstruction in the mid-latitudes of the Northwest Pacific in the Early Cretaceous.