松本盆地の第四紀地質 : 松本盆地の形成過程に関する研究(3)

概要

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A wide-spread lake assumed to be larger than the recent Matsumoto Basin had existed in Early Pleistocene, and the Enrei Formation and its equivalent formations had been deposited in the lake. An extensively even erosion surface formed on the sediments in the latest Early Pleistocene is called the Ohmine geomorphologic surface. After the formation of the Ohmine surface, the recent mountainous areas such as the Northern Japan Alps, Mt. Hachibuse, Mt. Utsukushigahara and so on had been upheaved, while the Matsumoto Basin area had been depressed and the Nashinoki Gravel Formation, the upper Middle Pleistocene, had been deposited. The base of the Enrei Formation is 1,800 m above sea level in Mt. Hachibuse, while 700 m above sea level in the southern part of the Basin. The amount of upheaval of the mountainous areas can be estimated to be more than 1,000 m. The Matsumoto Basin area had been depressed again in the middle part of the Upper Pleistocene (about 40,000 years B. P.) and the Hata Gravel Formation had been deposited. The amount of depression may be estimated to be about 150 m in the eastern periphery of the middle part of the Basin.
日本地質学会の論文
1977-02-21