Abstract
Succession of the Middle Miocene to Pliocene series distributed in this area corresponds to the standard succession of the Niigata sedimentary basin, but is complex because these series include larger amounts of volcanic rocks than that of type area and still remain unknown.
From detail field and biostratigraphical study, and fission track dating, the succession and age of the Nanatani, Teradomari and Shiiya formations of the Miocene and the Nishiyama Formation of the Pliocene were clarified.
Biotite-hornblende dacite and hornblende andesite (9.0Ma) of the Teradomari Formation are interbedded with siltstones deposited in sedimentary environment of upper to middle bathyal zone and pyroxene andesite of the Shiiya Formation are interbedded with siltstones and sandstones deposited in the same environment as the Teradomari Formation. The Teradomari Formation is considered to has deposited on the Nanatani Formation which has occured as topographical high, resulting in clinounconformity between the two formations. The Nokogiriyama fault, which is main geological structure and is related to the Nigoro anticline, may has began to occur in the Shiiya stage as shown in defferences of lithofacies between both flanks of the Nigoro anticline.
