HOMOGENEOUS CHARACTERISTICS OF THE PARTICLE SIZE DISTRIBUTION AND MINERAL COMPOSITION OF A TUFF BED

Abstract

Tuff in sedimentary sequences provide useful key beds. Volcanic ash and dust from a single eruption can cover an extensive area in a very short time proving good continuity and homogeneity in key beds as regards to fades changes in associated sediments. Identification of individual tuff beds may be based on texture mineral composition. Such variations in texture and composition as do occur within individual beds depend on distance from source and wind conditions, but within short distances variations are slight. A study was made for particle size distribution and mineralogy of 16 samples over a distance of 70 km from a single tuff bed in Pliocene sediments of the Boso and Muira peninsula, Japan. Good homogeneity was found throughout. Other tuff beds in the same sequence could be clearly distinguished on the basis of texture and mineralogy.