Abstract
A meter-scale, bedded red radiolarian chert block was found on the Yo-oka Beach at the eastern edge of the Mineoka Belt, Boso Peninsula, central Japan. The block is included in the area composed of fragments of the Mineoka ophiolite and other sedimentary and igneous rocks, including a Paleocene to Miocene pelagic limestone/chert sequence. The radiolarian fauna indicates an assemblage zone of middle to late Albian (Early Cretaceous), partly corresponding to the age of the Tethyan fauna. The tectonic significance of this Cretaceous radiolarian chert block is not clear: it could be from either the Mineoka ophiolite and related oceanic plate stratigraphy or from the Shimanto Supergroup.
