Abstract
This study aims to reconstruct shelf environment of the Lower Triassic Osawa Formation in the Inai Group, the South Kitakami Terrane (SKT), on the basis of the vertical variations of chemical composition and ichnofacies. The Osawa Formation in the Ogatsu area is divided into the lower part (OL ; intensely bioturbated calcareous siltstones) and upper part (OU ; parallel laminated mudstones). The redox proxies (Zn/TiO2 and Ni/TiO2 ratios) and the benthic activity proxies (ichnofabric index and burrow diameter) suggest that the OL was deposited in a shelf where benthic activity was very high, whereas the OU was deposited in a relatively reductive environment that prevented benthic activity.
