Significance of the direct correlation of ammonite and radiolarian zones in the Izumi Group for integrated biostratigraphy of Late Cretaceous NW paleo-Pacific region

The direct correlation of radiolarian and ammonite zones in the Izumi Group were reviewed and revised for integrated biostratigraphy across the Campanian – Maastrichtian boundary. The significance of the direct correlation between mega- and micro-, i.e. between relatively near-shore nektonic and slope-basin planktonic faunas in the same stratigraphic field, was discussed in relation with the litho- and biofacies of the group. The Late Cretaceous ocean climate change and surface seawater current inferred from the radiolarian fauna was considered as a marker event for the chronostratigraphic correlation in the middle latitude continental shelf to slope-basin facies facing towards the NW paleo-Pacific.