たい積物中の火山ガラスの研究 大阪平野の更新〜完新統について

Abstract

The Pleistocene to Holocene sediments underlying the Osaka Plain consist of unconsolidated gravels, sands, silt and clay beds of limnic, fluvial and marine origin.IKEBE et al. (1970) and FURUTANI (1978) described the subsurface geology of the Osaka Plain is through the investigation of the drilling cores. From these studies the subsurface stratigraphy of the Osaka Plain summarized as the following sequence, the latest Pleistocene to Holocene formation (Nanba Formation), the upper Pleistocene formation (Ma 11 bed, Ma 12 bed and Tenma Formation) and the Osaka Group in descending order (Figs. 1 and 2).The writer investigated the content of glass fragments in these sediments and also studied the features such as shape and refractive index of glass fragments.The results obtained are the following:1) The content and the features of glass fragments from the Pleistocene to Holocene sediments are shown in Fig. 3, 4, 5, 6, 7, 8, 9, and 10.2) On the basis of the vertical variation-diagram (Figs. 3…10), volcanic ash- horizons can be found in these sediments, because the vertical variations of content and features of glass fragments are controlled mainly by the fall of volcanic ash.3) Five volcanic ash-horizons occur in these sediments and are widely traceable. Among these five horizons, three horizons are in the Ma 12 bed, and two horizons are in the Nanba Formation.4) The lower ash-horizon in the Nanba Formation can be correlated with the ash layer described by MAEDA (1976) in Core Site 2. The upper ash-horizon in the Nanba Formation can be correlated with the ash layer described by ISHIDA et al. (1969) in the Kyoto Basin.