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GeoDigital Information's study of the Muddy Sandstone of the Northern Powder River Basin examines the stratigraphy, sedimentology, petrography, and oil and gas potential of the Muddy Sandstone in the northern part of the Powder River Basin. This area covers approximately 231 townships and more than 8,300 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 Statigraphic 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 northern part of the Powder River Basin.

MUDDY EXPLORATION TRENDS - Exploration interest in the northern portion 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 northern part of the Powder River Basin.

Database

3092	Study Wells	164	Cores Described
7637	Wells with Shows, Core Footages, Production	150+	Thinsections
17	Regional Stratigraphic Markers Correlated	59	Outcrops Measured

Maps

Regional Maps	Field Maps
Isopach Maps Net Sandstone Map Structure Map Study well Map	Isopach Maps Net Sandstone Maps Structure maps

Cross Sections		Field Studies
5	Regional Stratigraphic Sections	Ute Amos Draw, Collums-Morse,
22	Field Cross Sections	Store-Oedekoven, Kitty

Report Contents

TEXT AND FIGURES-An extensively illustrated report includes discussions, figures, and color plates on: Executive Summary, Depositional Setting, Lithofacies, Stratigraphy, Depositional History, Petrography, Field Studies, Synthesis, and Exploration Potential.	STRATIGRAPHIC DATA-This file contains the stratigraphic data (17 formation tops and stratigraphic markers, and net sandstone values) and isopach values, as well as information on well name, operator, location, API number, completion date, datum, and production status for the 3092 study wells.
CORE AND OUTCROP DESCRIPTIONS-This appendix contains descriptions of 164 cores from the study area. It also contains descriptions of 59 outcrop localities along the margins of the Powder River Basin.	MAPS AND CROSS SECTIONS-This appendix contains regional maps and field study maps. This includes isopach maps, structure maps, net sandstone maps, and a study well map.