Full Title: Tonsteins: Altered Volcanic Ash Layers in Coal-Bearing Sequences
Authors: Bruce F. Bohor and Don M. Triplehorn
Volcanic ash deposited and preserved in nonmarine environments alters to claystone layers called tonsteins. Their volcanic origin is confirmed by mineralogical and geochemical analyses and by characterization of their field relations. Because of their volcanic, air-fall origin, tonsteins act as widespread isochrons useful for correlation and radiometric dating. The authors define tonsteins and address geographical distribution and volcanic characteristics, propose diagenetic pathways for alteration of volcanic ash into tonsteins, and explain the influences of bed thickness, composition, and rates of flushing and water chemistry on the final product.