Abstract

Morphometric data (roundness and elongation) on Recent pebble associations can be used to determine whether the last effective abrasion of the pebbles prior to deposition in a shallow marine environment occurred in a littoral or a fluviatile environment. Only pebbles of chert, quartzite, and rocks of similar uniformity of composition and resistance to wear are suitable for such studies. Angular and subangular grades and irregularly shaped particles are largely eliminated from pebble associations of fluviatile and littoral origin; the degree of roundness tends to be greater in associations of littoral origin. Charts, prepared from data obtained from modern rivers and beaches in Japan, permit a paleoenvironmental interpretation of hard rock pebbles found in ancient conglomerates.

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