抄録
The pyroclastic deposits distributed widely around Kuttara Volcano are studied on the distribution, the chemical composition of orthopyroxenes by EPMA analysis, the refractive indices of minerals and glasses, and the X-ray diffraction and chemical analysis data of ferromagnetic minerals. The results of these studies are as follows. The pyroclastic deposis erupted from Kuttara Volcano are divided into the following various deposits in descending order : the Kt-a Pumice Flow, Kt-b1 Pumice Fall, Kt-b2 Pumice Flow, Kt-c Pumice Fall, Kt-d Scoria Fall, Kt-e Pumice Flow, Kt-f Pumice Fall, Kt-g Scoria Fall, Kt-h Pumice Scoria Flow, Kt-i Pumice Fall, Kt-j1 Pumice Fall and Kt-j2 Pumice Flow. These deposits are correlative with the tephras as follows; [table] N, Us-c Pumice Fall Deposits mainly spreading around Lake Toya were also erupted from Kuttara Volcano, and are named Kt-c Pumice Fall according to their stratigraphic horizon. These tephras contribute much as stratigraphic marker to the study of remarkably variable paleoclimate and paleoenvironment between Kuromatsunai Low-land and Tokachi Plain in Late Pleistocene.
