Cycle of Sedimentation in the Japanese Neogene

Abstract

In this paper the writer discusses the cycle of sedimentation as suggested by a study of Japanese Neogene deposits. The paper begins with a discussion of the geologic relations of crustal movements to the sedimentation cycle.
It is next, nexplained that three cycles of sedimentation exist in the Japanese upper Neogene. The following three cycles are expected in the succession of strata of the Japanese upper Neogene on ' the Pacific side of Southwest Japan and the Japan Sea side of Northeast Japan, and the southwest part of Hokkaidô: (1)“mm-mu”(upper Miocene) cycle; (2)“mu-pm”(uppermost Miocene-middle Pliocene) cycle; (3)“pu”(upper Pliocene) cycle. Then is discussed the chronologic relation of the“pu”cycle of sedimentation to the evolution of Umbonium suehieme Yoko.yama, as proposed by Prof. J. Makiyama.⁽⁴⁾ A close chronologic relation seems to exist between them. Umbonium suchiense subsuchiense Mak., which flourished in the beginning of the“pu”cycle, was soon succeeded by U. giganteum naganumanum Otuka⁽²¹⁾ during the same cycle. This replacement is observed in the basal part of the“pu”beds (“pu” and “pd”in the writer's previous paper) e. g. the Soga⁽²⁹⁾ beds (Totomi province), Higasihigasa beds of the Akimoto group (Kadusa), Ninomiya group, Naganuma beds, Tatibana group (Musasi province). Lastly the geologic age of the writer's Nisikoiso beds, Ninomiya beds, Naganuma beds, and the Tatibana group are discussed from the view of cycle of sedimentation. The writer's conclusion is that these formations are upper Pliocene.