東海層群の火山灰層とその対比

抄録

The Tokai Group, one of the representative Pliocene-Pleistocene sequence in the Second Setouchi Sedimentary Basin, is widely distributed around Ise Bay and composed of lacustrine and fluvial deposits such as gravels, sands and muds with many intercalations of volcanic ash layers. The volcanic ash layers of the Tokai Group in Chita, Kameyama, Yokkaichi and Inabe areas are petrographically investigated, and the following results are obtained. 1) Petrographic characteristics of each ash layer are summarized in Table 1. 2) On the basis of the tephrostratigraphic, lithologic and petrographic data of the volcanic ash layers, the Tokai, Kobiwako and Osaka Groups are correlated with each other as shown in Fig. 4. The Otani vocanic ash layer of the Tokoname Formation in Chita area is correlated with the Akogi volcanic ash layer of the Kusuhara Formation in Kameyama area. The Iwamori volcanic ash layer of the Kameyama Formation is correlated with the Ichinohara volcanic ash layer of the Kono Formation in Inabe area and also the Masugi volcanic ash layer of the Kobiwako Group around Lake Biwa. The Chomyoji E volcanic ash layer of the Kameyama Formation may be correlated with the Minamidani-1 volcanic ash layer of the Ichinohara Formation in Inabe area, the Sagami I volcanic ash layer of the Kobiwako Group and the Habutaki I volcanic ash layer of the Osaka Group around Osaka Bay. The Nagasawaand Koyashiro volcanic ash layers of the Sakuramura Formation in Kameyama area can be correlated with the Komazuki and Mushono volcanic ash layers of the Kobiwako Group respectively. The Kawashima n volcanic ash layer of the Hachioji Formation in Yokkaichi area is correlated with the Bando-1 volcanic ash layer of the Ichinohara Formation in Inabe. The Karegawa volcanic ash layer of the Oizumi Formation in Inabe area, which is the most useful marker bed in the Tokai Group, is correlated with the Gokenjaya volcanic ash layer of the Kobiwako Group and the Fukuda volcanic ash layer of the Osaka Group. The Tara volcanic ash layer of the Oizumi Formation is correlated with the Pink volcanic ash layer of the Osaka Group.