Tephrostratigraphy and petrology of subaqueous ashes in the northern Fossa Magnaregion.

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Field survey on subaqueous ashes in northern Fossa Magna region, and upper Miocene to lower Pleistocene tephrostratigraphy in this region was established. Correlation of tephras was made by means of field survey, laboratory investigation of their componernts and EPMA analyzes of volcanic glass shards.Major correlative conclusion is as followsi(1)lower Pleistocene Ogash in Niigata region is correlative to Osaka Pink ash.(2)lowernost T2c ash in Niigata region is correlative to Kd38 ash in the Boso Peninsula.(3)Pliocene Arg-2 ash in Niigata region is correlative to Habutaki I ash in the Osaka Group.(4)lower Plioune Znp-Ywg ash in Niigta region is correlative to PM ash in the Himi Group and Otani ash in the Tokai Group.(5)Upper Miocene Ndp ash in the Niigata region is correlative to the upper part of the Susobanatuff in Nagano region, northern Fossa Magna.