Abstract
This study clarified the stratigraphy of the Miocene series that occur in contact with pre-Neogene basement rocks in the Echigo-Yuzawa region. Based on new lithologic assemblages, the Miocene stratigraphy and the tectonic process of the Echigo-Yuzawa Basin were reconstructed. The Miocene formations are distributed in the Shiozawa and Tsuchitaru areas in the Echigo-Yuzawa region. The Shiozawa area comprises the newly proposed Shiozawa Formation (Maiko Breccia Member, Yoshiyama Shale Member and Komatsuzawa Basalt Member) and the Tsuchitaru area comprises the redefined Matsukawa Formation (newly proposed Tsuchitaru Sandstone and Basalt Member, Nakazato Tuff Member and Kandatsu Shale Member). A new record of planktonic foraminifer indicative of Blow's N.9 (Blow, 1969) was discovered from the Kandatsu Shale Member. The tectonic development of the Miocene Echigo-Yuzawa Basin is as follows : [Stage I] Basin generation due to collapse, forming a lacustrine lake (18-17 Ma).[Stage II] Subsidence accompanied with marine transgression and bimodal volcanism (17-15Ma).[Stage III] Continuous subsidence depositing mud (15 Ma).
