The Lower Cretaceous Muddy Formation can be recognized almost everywhere in the Wind River Basin. The Formation consists primarily of quartzose and chert bearing sandstones and siltstones, carbonaceous sandstones and siltstones, fine-grained conglomerates, black and gray shales, and brown lignitic shales. The sandstone bodies within the Formation are extremely local and lenticular in nature and are irregularly distributed. These lenses appear to represent both individual and coalescing bar, channel, and deltaic deposits. The Muddy Formation is believed to be a poorly developed eastward extending tongue of the Bear River Formation occupying the same stratigraphic position as the Newcastle Sandstone which is believed to be a westward extending tongue of the Dakota Group of eastern Nebraska. The vertical sequence of lithologic varieties, sedimentary structures, and wide-spread evidence of diastems and local angular unconformity suggest that the sediments of the Muddy Formation were deposited in the shallow shoaling waters of an eastward regressing and subsequently westward transgressing Early Cretaceous sea. Evidence indicates that most of the sediments were deposited in a transitional environment, some are certainly of marine origin, and some may represent fluviatile conditions.
Proceedings of the Iowa Academy of Science
©1962 Iowa Academy of Science, Inc.
Whiteford, Stanley D. Jr.
"Regional Aspects of the Muddy Formation in the Wind River Basin, Wyoming,"
Proceedings of the Iowa Academy of Science, 69(1), 411-430.
Available at: https://scholarworks.uni.edu/pias/vol69/iss1/65