著者

長田 敏明

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.19, no.1, pp.1-14, 1980-05-31 (Released:2009-08-21)

参考文献数

27

被引用文献数

2 2

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The subject of this paper is to establish the stratigraphy of deposits composing to Makinohara Upland, and also to discuss the landform evolution of the Makinohara Upland. The results are summarized as follows:(1). The terrace-forming deposit is divided into three beds, i.e, Furuya mud bed, Kyomatsubara sand bed and Makinohara gravel bed in ascending order.(2). The Furuya mud bed accompanied with the basal gravels is mainly composed of marine silt and clay filling the buried valleys (Fig. 10 and Tab. 1). The main part of the Furuya mud bed deposited in the narrow drowned valleys, during the early stage transgression, and covered uncomformably the Neogene semiconsolidated rocks.(3). The Kyomatsubara sand bed newly defined by this author was widely deposited in this mapping area as foreset beds at the maximum phase of the transgression (Fig. 9).(4). The Makinohara gravel bed mainly consists of widespread homogeneous fluvial gravels, the upper part of which is boulder gravel forming the alluvial fan named Makinohara.(5). Five horizons of buried topographic system are found under the Makinohara Upland; Buried surface I, II, III and IV (Figs. 8, 10) and Buried valley floor.(6). The Buried valley floor is the oldest topographic system filled with the Furuya mud bed. Two horizons of abrasion platforms (Buried surface I and II) are found cutting the slope of buried valley systems. The Buried surface I was formed just after the deposition of basal gravel of Furuya mud bed. The Buried surface II, on the Neogene strata was formed during the accumulation of upper mud part belonging to the Furuya mud bed (Fig. 10).(7). The Buried surface III covered with the Kyomatsubara sand bed is the most extensive among the three buried abrasion platform cutting the Neogene strata (Fig. 8 and 10).The level of the boundary between the Furuya mud bed and the Kyomatsubara sand bed nearly corresponds with that of the Buried surface III.(8). The Buried surface IV is the basal topography of the Makinohara gravel bed. Finally extensive rivers, laterally eroding the valley slope flew down onto the newly emerged coastal plain and slightly cut the Kyomatsubara sand bed (less than 5m) (Fig. 10). At that time, the Buried surface IV was formed as a basal topography of the Makinohara gravel bed.(9). The Makinohara Upland was constructed as alluvial fans by the Paleo-Oi River. The deposits forming the Makinohara Upland are defined to the Makinohara gravel bed.