On the Geology of the Eastern Border of the Shizukuishi Basin

The stratigraphic sequence and lithological characters are as follows, in descending order ; Pleistocene Masuzawa formation (?) : alternation of laminated tuff～shale and tuff. Yabitsu formation (200m) : upper part, alternation of tuff breccia and tuffaceous shale. lower part, alternation of shaly tuff and tuff breccia～tuffaceous sandstone. Osuke formation (300m±) : massive tuff breccia. Shimosaruta formation (110m+) : alternation of sandy tuff and laminated tuff～tuffaceous shale. (Betula cfr. miomaximowicziana Endo, Alnus cfr. protohirsuta Endo, etc). Iioka formation (250m±) : two pyroxene andesite and its agglomerate. Palaeozoic formation : hornfels, chert, etc. The geological structure is complicated and many faults and folding structures were noticed. Faults are classified into three systems, namely (1) outside fault system, (2) inside fault system and (3) intermediate fault system. Outisde fault system is composed of at least two or three parallel arc-shaped faults, and divides the Ou mountain chain from the Kitakami lowland. Inside fault system is composed of an arc-shaped fault and a straight fault of N-S direction, and forms the boundary between the hilly mountains on the basin bottom and surrounding steep mountains