Geomorphological Study in Kawasaki Basin, MiYagi Prefecture

Abstract

The writer studied three basins which belong to the catchment area of the Natori River. The surroun-ding area are the table lands of tertiary formation composed of the Takadate andesite, liparite and the marine and Paleo-lake deposits. The Kawasaki Basin of rectangular form lies between the Takadate and the Akyu table lands, and the slender Hasekura basin and the complicated Tsubonuma-Sugo basin in the latter. Near them the two tectonic lines, named Nagamachi-Rifu and Hisanohama and Iwanuma, run or the east bounding the table lands form the Sendai coastal plain, and another one of importance meaning is the Murata thrust fault in the southwestern part of the Takadate table land. After surveys in the field, the writer concluded as follows. 1) All the three basins are the tilt block basin by Jhonson (or the fault angle depression by Cotton). No fault lines have been informed by geolagist, but the topographical features prove the dislocation. The evidences in the Kawasaki basin are the presence of the terminal facets and the fans and the narrow disturbed zone of the formation along the linear margins of the basin (the two sides of it having the different formation). In the Hasekura basin, the steep and linear northwestern slope is contrary to the gentle and comlicatec southeastern slopes with the terminal facets and the geology and the surface geology differ between then (the gravel bed in the case of the former and the loam in the latter). In the Tsubonuma-Sugo basin, the dislocation is supposed form the displacement of the plane of the surrounding table lands and the steel diffs of the western margin which prolongs to the Murata Fault. 2) The Kawasaki basin and the Tsubonuma-Sugo basin are the lake basin. In the former, two group of the horizontal patches (180m and 220m above sea-level) are dominantly adhered to the hill in the basil and further its corresponding delta sediments and deposits are observed in the western part. In the latter, the thick clay deposit and peat show the fact of the lake at the cottom.