信州地域の第四紀層 : とくに,鮮新・更新統と中部更新統について  [in Japanese] Quaternary Stratigraphy in Shinshu, Central Japan : on the Plio-Pleistocene and Middle Pleistocene  [in Japanese]

Shinshu is situated in center part of Honshu Island, where is composed of Fossa Magna area and east part of West-South Japan. Quaternary Systems are distributed mainly in the inland-basins and volcanic areas. Inland-basins are situated in side and outside of Fossa Magna. Those basins have been covered with the wide alluvial plains consisted of fan deposits. Another distribution area of Quaternary System in Shinshu is the volcanic area. Those are lain under the slope of the volcanic body such as Mt. Yatsugatake, Mt. Ontake, and Mt. Kurohime. The thich Quaternary Systems are extensively distributed, for the reason that the lake basin had been formed in advance of the volcanic activity. Those Quaternary Systems were accurately correlated each other by the wide spreaded volcanic ashes. Lower Pleistocene series in Shinshu distribute in the sedimentary basins formed after Neogene. Sarumaru Formation, one of the representative Plio-Pleistocene series in Shinshu was formed in sedimentary basin of Northern Fossa Magna. Plio-Pleistocene boundary is located in the Upper Menber of this formation. Yachiho Group is also Plio-Pleistocene series and conformably overlains in Komoro Group which belongs to the Pliocene series. Yachiho Group deposited in the lake basin which was formed before the volcanic activity of Palaeo-Mt. Yatsugatake. At the last stage of the Early Pleistocene, the wide peneplains were formed. Ohmine Plainis such a Plain, and on the surface of this plain, granit boulders are distributed, which were carried from the Hida Range side passing through the Matsumoto Basin, which had been holizontal plain with Ohmine Plain are. So that, Matsumoto Basin not yet formed at that time. Matsui Plain on the slope of the Mt. Yatsugatake was also formed at last stage of the Early Pleistocene, and covered with Matsui Decayed Gravel Formation. Almost of Inland basins of Shinshu was formed during the Middle Pleistocene. Along the edge of these basins, the high terraces composed of Middle Pleistocene are distributed. These terraces had been leaved from relative subsidence of the basin. Nashinoki Gravel Formation is a typical sediment or such terraees, and intercalates the wide spreaded volcanic ash as C_1〜C_4 (=A-Pm), which can traces to Nagano Basin and Yatsugatake area. Minamisaku Group was formed in the Lake basin around Mt. Minami-Yatsugatake. This basin was formed unconformably on the Matsui Decayed Gravel Formation, and center of this basin was shifted attended for the moving of the center of volcanic activity.