Abstract
The Katata Formation, which is the upper part of the Kobiwako Group, is distributed on Katata Hill. This formation intercalates with the Kamiogi I volcanic ash bed, which is a useful key bed for the Middle Pleistocene formations because it is equivalent to the Ks11 tephra bed in the Kazusa Group on the Boso Peninsula. Some tephra beds above this volcanic ash bed are newly described herein. They are named the Ikadachi I, Ikadachi II, and Yamanoshita volcanic ash beds, in ascending order. These tephra beds are correlated with tephra beds in the Kazusa Group on the basis of their petrographic properties, chemical compositions of volcanic glass shards, and stratigraphic positions. The volcanic ash beds Kamiogi II and Ikadachi II in the Kobiwako Group are correlated with the Ks10 and Ks5 tephra beds in the Kazusa Group, respectively. Additionally, the Yamanoshita volcanic ash bed is correlated with K1-175 in the Higashinada 1,700m core taken from Osaka Bay, because 1) their properties are similar and 2) they are both above the abundance bed of Quercus subgen. Cyclobalanopsis. Their estimated ages show that the Katata Hill area was a depositional area until 350 ka at least.
