大阪ピンク火山灰と新潟地域の小木火山灰との対比

概要

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The lower Pleistocene Ogi ash in Niigata region is correlated to wide spread Osaka Pink ash in the Osaka Group, Kinki district. The Ogi ash is vitric ash of 17cm thick, pink in color, and intercalated in the lower Pleistocene Haizume Formation and Uonuma Group. Both the Ogi and the Osaka Pink ashes are in the lower level within the Jaramillo event of about 1 Ma. Lithological and petrographical characteristics of the Ogi ash are completely similar with those of the Osaka Pink ash, such that the shape of glass shards, heavy mineral association (hornblende > orthopyroxene, iron ores, clinopyroxene, zircon > apatite), refractive indices of glass shards (n=1.498-1.502), hornblende (n_2=l.673-1.678) and orthopyroxene (γ=1.700-1.710), and chemical composition of volcanic glass. Lithologic unit association of the two ashes are almost similar, and grain-size decrease in the Niigata region is more notable in the coarser unit compared with the finer ones. The Osaka Pink ash has been correlated to co-ign-imbrite ash of the Yabakei pyroclastic flow from the Shishimuta caldera, Central Kyushu. Thus, the Ogi ash in Niigata region has been derived from 800km away southwest ward.
地学団体研究会の論文
1994-09-25