Geology and accretionary age of the Otori Unit, North Kitakami Belt

The North Kitakami Belt in Northeast Japan mainly comprises accretionary complexes formed during the Jurassic to earliest Cretaceous. complex of is less studied compared age-equivalent Southwest Japan. Here, we provide additional data on formerly classified as Otori Unit, distributed northeastern part upper reaches Akka River Iwate Prefecture. Based detailed field mapping, clarified that Unit composed structurally lower coherent facies chert and siliceous mudstone (Okoshizawa Subunit) mixed mudstone, sandstone, minor basaltic rocks (Osakamoto Subunit). Manganese nodules from within Okoshizawa Subunit yielded radiolarians indicating Bathonian (upper Middle Jurassic). Detrital zircon grains sandstone Osakamoto has a youngest age ~170 Ma (YC1?: 171.8 ± 2.4 Ma; YSG: 170.9 3.8 Ma). radiolarian detrital ages, estimated Bathonian. Our new were also considered discuss correlation between Southern Chichibu corresponds Ohirayama structural position, two units are similar being have overlapping age. However, lacks limestone considerably younger for suggesting may not be strictly correlative.