THE STRATIGRAPHY AND ENVIRONMENTS OF DEPOSITION OF THE CRETACEOUS HELL CREEK FORMATION (RECONNAISSANCE) AND THE PALEOCENE LUDLOW FORMATION (DETAILED), SOUTHWESTERN NORTH DAKOTA

摘要

The Cretaceous Hell Creek and Paleocene Ludlow Formations of southwestern North Dakota, with the exception of the included lignite beds and minor amounts of concretions and nodules, arc almost exclusively classic sediments and sedimentary rocks. Massive clays, clays alternating with silts and sands, sandstones filling channels and other depressions, sheet sandstones, and lignites are the dominant sediment and rock types present. These sediments and sedimentary rocks were mostly deposited in a continental environment and were largely alluvial, lacustrine or paludal in origin;though marginal marine deposition, in part, is indicated by the occurrence of brackish water faunas in portions of the upper Ludlow Formation.nWith the possible exception of a persistent lignite near the base, persistent lignites are not present in the Hell Creek Formation.