Age of the Itoman Formation (new to science) at base of the Ryukyu Group in southern part of the Okinawa-jima, Ryukyu Islands, Japan.

Abstract

The Itoman Formation is newly proposed and described herein, that called "reddish limestone" in Kaneko (1994), Kaneko and Ito (1995, 1996). Age of the Itoman is estimated about 1.3 Ma from strontium isotope stratigraphy. The Itoman is a basal formation of the Ryukyu Group, consisting of coral reef complex deposits and related formations. A depositing period of the Itoman is the first stage of coral reef development around the Ryukyu Islands. The estimation of the age of the Itoman is important to establish a tectonic history of the Ryukyu Islands and coral reef development.