1987 年 26 巻 1 号 p. 69-78
Three tephra horizons were recognized at Itai Archaeological Site, Hyogo Prefecture, from the quantity distribution of volcanic material (mainly volcanic glass shards) and the refractive index of three columnar sequence samples. They are named Itai-Lower, Itai-Upper and Itai-Uppermost tephra horizons, in ascending order.
The three tephras are correlated with BB 55, BB 51 and BB 15 volcanic ash layers (in ascending order) in the 200m drilling core samples of Lake Biwa, and also can be correlated with the previously studied widespread tephras: Aira-Tn (AT), Daisen-hoki and Kikai-Akahoya (K-Ah) ashes, respectively.
Paleolithic tools were found at the three horizons as follows.
(1) Below the Itai-Lower tephra horizon, stone tools consist mainly of awl-like tools of sanukite, and include knife-shaped tools, scrapers, retouched flakes, hammerstones and cores.
(2) Between the Itai-Lower and Itai-Upper tephra horizons, stone tools consist mainly of knife-shaped tools made of elongated flakes and wide-flakes, and include edge-ground ax-shaped tools, scrapers, retouched flakes, hammerstones and cores.
(3) Between the Itai-Upper and Itai-Uppermost tephra horizons, a tanged point was found.
Based on the tephra correlation and 14C ages obtained from the site, ages of Paleolithic tool horizons at Itai Archaeological Site are determined to be approximately 22, 000y.B.P., 21, 000-20, 000y.B.P. and 20, 000-6, 300y.B.P., in ascending order.