Composition and properties of the Pierre Shale and equivalent rocks, northern Great Plains region

Abstract

The Pierre Shale and equivalent rocks of Late Cretaceous age con sist in the east-central Dakotas of several hundred feet of offshoremarine shale and minor marl; in west-central Montana near the sedi ment source the equivalents of the Pierre Shale consist of several thousand feet of volcanic-rich and mostly nonmarine sediments; and in the area between, both types of rock are separated by tongues of nearshore-marine siltstone and sandstone that mark three major transgressions of the sea across the area. The major-, minor-, and trace-element composition was determined for 226 samples of these rocks, and the mineralogical composition was determined for 1,350 samples. Slurry pH, Atterberg limits, and grain and bulk densities were determined on some samples.