東北・関東地方の海成第四系

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The boundary between the Pliocene and Pleistocene has been defined in the stratotype Vrica section in southern Italy. The boundary is extended to a horizon between the marker tuff beds Kd20 and Kd25 in the lower part of the Kiwada Formation of the Boso Peninsula, Japan. The Pleistocene will be subdivided into three parts. The Lower/Middle and Middle/Upper boundaries in the Pleistocene correspond to the geomagnetic polarity transition from the Matuyama Reversed to Brunhes Normal Chrons and the last high stand of sea-level in the Pleistocene, respeetively. The marine Lower Pleistocene sediments, together with the Pliocene, composes the hills, the Middle Pleistocene marine sediments occur in the middle terraee formation, and the marine Upper Pleistocene is the basal to middle part of the coastal plain formations in the Pacific coastal areas of Tohoku Region, as well as in some other areas in Japan. Combined bio- and magnetostratigraphy makes it possible to correlate the marine Pleistocene to the global extent, but some problems have been still unsolved in the correlation between marine and terrestrial sediments. Among others, the relation of marine magnetostratigraphy accompanied by biostratigraphy to magnetic chronology accompanied by numerical age determination should be reexamined. By the recent fission track dating on the volcanic ash layers in the Boso Peninsula and Kinki Region, the "Olduvai" Subzone and "Gauss" Zone inferred in marine sections are most likely corresponded to the Gauss Chron and a part of Glibert Chron, respectively, in the Cox's scale. The Lower to Middle Pleistocene of the Kanto Region is in on-lap sequence, which is deviated from general trend in accumulation, owing to regional subsidence during deposition. The subsidence began in the Pliocene by huge submarine slumping towards south, which involved almost whole Kanto Region and exerted influence on the Pacific areas of Tohoku Region. The unconformities at the top of the Kurotaki Formation in the Boso Peninsula and the top of the Tatsunokuchi Formation in the Sendai area represent the slumping of the Kanto Region and its derivation in the Tohoku Region.
日本地質学会の論文
1988-04-25

東北・関東地方の海成第四系

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