Memoir 17—Geology of Pennsylvannian and Wolfcampian rocks in southeast New Mexico

By R. F. Meyer, 1966, reprinted 1985, 123 pp., 15 tables, 76 figs., 4 plates, 1 index.

The area of this study includes about 38,700 mi² in southeast New Mexico that lie within the Great Plains physiographic province on the east and the Basin and Range province on the west. Pennsylvanian and Wolfcampian rocks are discontinuously exposed in the mountain ranges on the west and in boreholes elsewhere.

Major positive elements of the area during Pennsylvanian and Wolfcampian time included the Pedernal uplift, which extended in a north-south direction through the center of the area, and the Central Basin platform, the northwest corner of which lay in the southeast part of the area. Minor positive features included the domical Roosevelt uplift in the northeast, the Oscura and Joyita uplifts in the northwest, and the Diablo platform in the southwest. Major negative elements were the Permian Basin on the east and the Orogrande Basin on the west. Subprovinces of the Permian Basin were the Northwest shelf and the Delaware Basin, which included the Salt Flat embayment. Subprovinces of the Orogrande Basin were the Robledo and Sacramento shelves. The Orogrande Basin merged northward with the extreme south end of the Estancia Basin, and in like manner the Permian Basin joined the Tucumcari Basin.

Pennsylvanian and Wolfcampian rocks are subdivided into stages based upon biostratigraphic zones defined by occurrences of fusulinids. It is possible to trace the zones over the entire area, thus effecting correlation of subsurface occurrences with outcroppings of rocks of the same age. The Pennsylvanian System here includes, in ascending order, the Morrowan Stage of the Lower Pennsylvanian Series, the Derryan and Desmoinesian Stages of the Middle Pennsylvanian Series, and the Missourian and Virgilian Stages of the Upper Pennsylvanian Series. Permian rocks described are those of the Wolfcampian Stage, (Lower Permian series).

Prior to Pennsylvanian time, the area was the site of a shelf across which were deposited Cambrian, Ordovician, Silurian, Devonian, and Mississippian sediments in seas entering the area from the south. Post-Chesteran uplift on the north resulted in southward tilting, and erosion, of pre-Pennsylvanian rocks. Pennsylvanian strata were deposited across Mississippian rocks to the south and on progressively older rocks northward, where Precambrian is exposed. In pre-Morrowan time, the Pedernal uplift was formed, which divided the area into two parts throughout the balance of the Pennsylvanian.

Morrowan rocks are the most areally restricted of the various stages and contain the largest proportion of coarse clastic material. They attain thicknesses of 1,250 ft in the Permian Basin and 750 ft in the Orogrande Basin. Topographic relief over the Pedernal uplift was probably at a maximum during this time, most pre-Pennsylvanian sediments being eroded from it. Erosion of the granite core provided quartzose sandstone to the basins.