Diagenesis of tuffs in the Barstow Formation, Mud Hills, San Bernardino County, California

Abstract

The Barstow Formation of Miocene age consists chiefly of lacustrine and fluviatile clastic rocks. Lacustrine rocks are mainly mudstone with interbedded tuff and carbonate rocks. The tuffs make up about 1-2 percent of the stratigraphic section and are the most conspicuous and continuous strata. Most tuff layers are less than 1 foot thick, but some are as much as 7 feet thick. All tuffs were originally silicic, and most were vitric and fine to very fine grained. This report summarizes the physical properties, chemistry^ and genesis of those silicate minerals that formed in the tuffs during diagenesis.