A method for determination of volcanic glass concentrations in sedimentary sequences and its application to quaternary studies

A method for determination of volcanic glass concentration in sedimentary sequences is presented. This method consists of two steps: (1) systematic extraction of volcanic glass particles from samples taken at close intervals in a sedimentary section, and the determination of their concentration; (2) precise measurement of the refractive indices of the separated glass particles. A recently developed measuring system (RIMS 86) based on the thermal immersion method permits quick and accurate measurement of the refractive index of a large number of grains within samples. Based on these kinds of data, we typically recognize five types of concentration of volcanic glass shards in sedimentary sequences. The method proposed here enables the simultaneous determination of the refractive index of glass shards and the proportion of glass shards in a sample, which makes it possible to recognize certain ash-fall-horizons, even those undetectable through visual observation of a sedimentary column. © 1994 John Wiley & Sons, Inc.