ABSTRACT

Deposition and distribution of Lower Pennsylvanian in Wyoming were affected by positive areas east and west of the state and in northeastern (Black Hills region) and southeastern (Laramie Mountain region) Wyoming. During Middle and Upper Pennsylvanian, uplift on the west became more intense and great thicknesses of clastics were deposited. The sea retreated eastward, and western and northern Wyoming became land, remaining so throughout Lower Permian. During that time a large part of southeastern Wyoming was a subsiding area. Vigorous uplift of the ancestral Front Range began in Middle Pennsylvanian and exerted influence on Wyoming sedimentation into Lower Permian. The Laramie Mountain region was a northward prong of this element.

The Black Hills are reflected by thinning of post-Osagian-pre-Desmoinesian deposits. Continuous deposition apparently occurred in the Hartville region from Morrowan(?) to Leonardian with development of a Wolfcampian anhydrite basin.

Evidences of these uplifts are revealed from study of the Amsden, Tensleep, Casper, and Hartville formations. It is suggested that the Tensleep be accorded formational status and include all units below the Permian redbeds and above the Amsden cherty carbonate rocks. The Casper formation of the Laramie Mountains is tentatively divided into lower, middle, and upper divisions approximating Middle and Upper Pennsylvanian and Lower Permian. Sandstone units were derived from erosion of the Ancestral Rockies and the Tensleep of northern and western Wyoming.

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