GeoDigital Information's study of the Muddy Sandstone of the Southern Powder River Basin examines the stratigraphy, sedimentology, petrography, and oil and gas potential of the Muddy Sandstone in the southern part of the Powder River Basin. This area covers approximately 396 townships and more than 14,250 square miles. The study, representing six man-years of geologic research, provides the explorationist with a chronostratigraphic framework for the lower Cretaceous Thermopolis, Muddy, Shell Creek, and Mowry formations. Also included in the study is a sedimentologic and reservoir characterization analysis of valley-fill deposits.

Lower Cretaceous Stratigraphic Framework

    The Lower Cretaceous stratigraphy of the Powder River Basin consists of, in ascending order, the Cloverly and Lakota formations, Thermopolis Shale, Muddy Sandstone, Shell Creek Shale, and Mowry Shale. Seventeen formation tops or bentonite marker beds including seven members of the Muddy Sandstone were correlated and mapped throughout the study area. Regional cross sections tie stratigraphic intervals throughout the study area of the Powder River Basin.

     Although rarely greater than 100 feet thick throughout most of eastern and central Wyoming, GDI subdivided the Muddy Sandstone into seven mappable, chronostratigraphic members, which are bounded by bentonite beds or unconformities. This chronostratigraphic methodology facilitated mapping of time-bounded lithofacies sequences and reconstruction of paleogeography through time. Of greatest importance was the recognition and mapping of a complex paleovalley system and marine shoreline trends within the southern part of the Powder River Basin.

Muddy Exploration Trends

     Exploration interest in the southern portions of the Powder River Basin was generated by numerous discoveries. The play consists of fluvial/estuarine valley-fill deposits. GDI's analysis of the stratigraphy, sedimentology, and petrographic characteristics is designed to assist exploration and production geologists in understanding the complex stratigraphic relationships, fluvial/estuarine valley-fill geometries, diagenetic history, and hydrocarbon production within the trend. The study discusses the potential for other valley-fill and marine shoreline trends throughout the southern part of the Powder River Basin.