Yokichi TAKAYANAGI2) Since the correlation between variations of the Earth's magnetic field and climatic changes first became an attractive subject for scientific study, much attention han heen given to the investigation of deep-sea sediment cores. Recently, the trend has been toward investigating increasingly minute subdivisions within the cores studied. Viewed from a micropaleontological standpoint, however, the size of the unit subdivision selected for study within the sediment core is of

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... vest import. In order to grasp the time significance and paleoecological implications of such subdivisions, some problems related to biostratigraphy and deep-sea sedimentation especially with respect to sedimentary disconformities, rates of sedimentation, the mixing of sediments by artificial as well as natural causes, and dissolution are reviewed.