福知山盆地の中部更新統

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The Fukuchiyama Basin is one of the small intermontane basins distributed in the Meso-Paleozoic terrain of the northwestern part of the Kinki District. The basin is filled with the Quaternary deposits having wide sedimentary surfaces which are regarded as the extensions of the"Higher Terrace"widely spreading in the central part of the Kinki. The followings have been clarified by the present studies.1) The Quaternary deposits in this basin reaches more than 50m in thickness consisting of five sedimentary units succeeded conformably, which are collectively called the Fukuchiyama Formation. Each unit was formed as a small fan developed along the marginal part of the basin or as fluvial deposit along the main river course flowing into the basin.2) Fig. 13 is the summary of the results of the studies of the Fukuchiyama Formation from viewpoints of paint fossil and paleomagnetism. No evidence of the Metasequoia flora was found, which shows that this formation is correlative to the Upper Part of the Osaka Group. The Sabia bed, intercalated in the upper horizon of the formation, contains the plant remains of warmer or subtropical types and is thought to correspond to the Ma 8 horizon of the Osaka Group.3) The paleomagnetic polarity of the Fukuchiyama Formation is normal except one narrow horizon showing reverse event. This is the character of the Brunhes Normal Epoch.4) The Fukuchiyama Formation closely resembles to the Meimi Formation in the Harima Basin in various points, which has a FT age of 0.49±0.09 Ma in the lowest horizon.5) The age of the Fukuchiyama Formation is inferred to be the Middle Pleistocene, about 0.6 or 0.7 Ma to 0.2 or 0.15 Ma, considering that the Brunhes Normal is generally dated 0.7 Ma to present with brief revesals at 0.11 and 0.02 Ma and Ma 8 horizon of the Osaka Group is intercalated with a volcanic ash layer having a FT ale of 0.38±0.04Ma.
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福知山盆地の中部更新統

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