Strontium isotopic age and the origin of including basalt pebbles of the Sashida Limestone in south Izu region, Japan

In the previous paper, geological ages of Late Cretaceous, Paleocene, late Middle to Eocene, Oligocene and early Early Miocene were confirmed at first time, based on occurrences both age diagnostic larger foraminifera associated planktonic foraminifera, from Sashida Limestone included basalt pebbles, Sashida, Kamo-Gun, south Izu Peninsula. Therefore, was made up clastic carbonate rocks various in essence as well outward form. this determination by microfossil re-investigated Sr isotopic same sample materials order get security. As a result, 69.3 71.8 Ma（Late Cretaceous; Maastrichtian）and 28.8 33.3 Ma（Early Oligocene；Rupelian）were determined supported partial. While, analysis chemical composition pebbles investigated estimate original generation tectonics. showed unique high magnesium alkali, similar basalts lower Yugashima Group assigned alkali series, which thought have emerged very stage Shikoku Basin spreading. The antecedent Peninsula defined landmass inferred lateral mobility toward east spreading, last, bordered north Honshu.