放射化分析による大阪層群・古琵琶湖層群の火山灰層の同定

概要

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The Plio-Pleistocene Osaka and Kobiwako Groups which are widely distributed around Osaka Bay and Lake Biwa in central Kinki district, are composed of gravel, sand and clay with many intercalations of volcanic ash layers. The volcanic ash layers found in both groups are valuable markers for research in regional stratigraphy and also play the most important role for interbasinal correlation, because such layers represent essentially instants of geologic time and deposits over a wide area. In this paper, 22 glass separates from 16 prominent volcanic ashes in both groups were analyzed by nondistructive instrumental neutron activation technique, with the purpose of characterizing each of the ashes on the basis of trace element contents. The results obtained are the following: 1) Data for contents of trace elements (La, Sm, Th and Sc) in glass separates are presented in Table 2. Concentrations of La, Sm, Th and Sc, and La/Sm ratios are found to be characeristic and serve as good discriminants for the volcanic ash layers examined in this investigation. 2) Trace element data from this study shows that Mitsumatsu, Fukuda (Fugenji) and Azuki ashes are very similar to Kiryu II, Gokenjaya (Gamodo) and Risen ashes respectively. These facts support the correlation of the volcanic ash layers between the Osaka and Kobiwako Groups proposed by YOSHIKAWA (1983).
1985-11-25