温海附近の地質と羽越地域における前期中新世のリフティング  [in Japanese] Geology of Atsumi area and Early Miocene rifting in the Uetsu district, northeast Japan  [in Japanese]

In the Uetsu district, Lower Miocene sediments which accumulated in narrow grabens are developed. They have large lateral variations in lithology, and show rapid thickness changes. The graben infills consist mainly of non-marine andesitic volcanics with trachytic ones. Fan delta and lacustrine facies are also common. Some of the grabens were bounded by growth faults along which debris flow deposits derived from basement highs are developed. The sedimentation rate was locally over 1 km/Myr during the syn-tectonic deposition. The Uetsu district submerged rapidly from non-marine environment to middle bathyal depth during the age of Blow's N.8 zone. Consequently, the subsidence rate was about 2 km/Myr during the submergence. In this article, stratigraphic and sedimentologic evidence of syn-tectonic sedimentation in Atsumi area is presented as an example of extensional tectonics in the Uetsu district. These tectonic features can be interpreted as rifting tectonics. The oldest graben infill in the district accumulated after ca. 22 Ma, possibly around 18 Ma. Black mudstone (Blow's N.9-10 zone) which accumulated in middle bathyal depth did not take part in the tilting but covered tilted blocks. Namely, the rifting ceased around Blow's N.9 zone.