The Nishikurosawa Formation contains many fossils of molluscas of a shallow sea type (IKEBE, 1963), and foraminifera of a warm sea type (IKEBE, 1962), and thick interbedded carbonates (!NOUE, 1977). The Formation unconformably overlies the underlying Formation. It is considered that the extent of the sediments of the Nishikurosawa stage attained to its maximum in Miocene transgression. Through this study, present authors clarified the relation between submarine volcanism and transgression in the Tsugawa-Aizu Province (SHIMAZU, 1973). The Tsugawa-Aizu Province having many collapse basins, which are 15-20 km in diameter, is characterized by the prevalence of submarine acidic volcanism in the Tsugawa stage. The Tenman Formation, conformably covers the underlying the Tsugawa Formation, and is composed of sandstone with alternatively intercalated mudstone, white pumice tuff and hard shale. The each member can be traced over the basins. The calcareous sandstone being intercalated in the alternation of mudstone and sandstone yields abundant foraminifera fossils indicating Blows' N. 8-9. In addition, the sandy mudstone of the lower member of the Tenman Formation in the Mikawa Basin yields Miogypsina-Opercurina (MAIYA, 1978). The Tenman Formation can be correlated to the Kamagui Formation which unconformably over-lies the basement rocks in the north district of the Niigata Sedimentary Basin. Above stated data indicate that the acidic volcanism in the Tsugawa-Aizu Province preceded the subsidence of the Niigata Sedimentary Basin. The sediments of the Tenman Formation correspond to those of the Nishikurosawa stage at the time of maximum transgression in Miocene age.
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