Partings and Stain by Clay of the Tsukumi Limestone

Abstract

The writers summarized the results of the survey and studies which were made since 1955 on the limestone of Tsukumi, Oita prefecture, especially refering to that of Oita mine. The major points of the results may be as follows.
A. The so-called "partings" of slate and greywacke, which are frequently composed of breccia of both rocks intermixed with fragments of limestone, have been found to be the anticlinal core composed of the rocks underlying the limestone bed. The partings have been crumpled or brecciated, and some parts seem to have been formed by the intrusion as a sort of breccia dike along the anticlinal axial plane.
B. From the distribution of the major partings on the surface, at least four anticlines have been detected in the Tsukumi limestone. The anticlinal axes gently plunge to NE, and where the group of major and minor anticlinal axes are zigzagged markedly in some localized area, the limestone in the area has been cracked and brecciated, and, moreover, the cavities thus formed have been stained by or filled with reddish brown clay.
C. The staining clay minerals are similar to the components of the surface soil of the limestone, being composed mainly of montmorillonite, halloysite, and goethite.
D. The part of the limestone low in phosphorous seems to make a definite stratigraphical zone, which suggests that this low P zone can serve as a key bed to dissolve the geological structure of limestone.