Paleozoic Stratigraphy of Franklin Mountains, West Texas

Abstract

The Franklin Mountains are within a region that is bounded on the east by Longitude 104° 30^prime W., on the west by Longitude 109° W., on the south approximately by Latitude 31° N., on the north approximately by Latitude 34° N. From just north of El Paso the Franklin Range trends almost parallel with the 106° 30^prime W. meridian to a point about 4 miles north of the Texas-New Mexico boundary. The Franklin Mountains are eroded block mountains typical of the Basin-and-Range province of southwestern United States. The west side constitutes a dip slope, while the east side is a scarp formed by a strike fault. The accompanying diagrams consist of a stratigram, which shows both the stratigraphy and the geographic location, and two columnar sections, one from Silver City, New Mexico, to El Paso, Texas, the other from the northern end of the Oscura Mountains in New Mexico to the southern end of the Franklin Mountains in Texas. The Paleozoic stratigraphic section is approximately 8,000 feet in thickness and includes Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian sediments. The Cambrian rests on the pre-Cambrian, which, in places, is represented by the Red Bluff granite (new name) and in other places by the Lanoria quartzite. The Magdalena formation is described in special detail. It consists primarily of thin-bedded, light gray to black limestone, which, for convenience, is divided into the following three members: the La Tuna at the base, the Berino, and the Bishop's Cap at the top. The characteristic fossils of certain members are listed. The Permian is represented by about 650 feet of exposed Hueco sediments. These sediments occur some distance west of the Franklin Range proper and are separated from the exposed Magdalena sediments by alluvial deposits. The contact between the Magdalena and the Hueco has not been seen in the Franklin Mountains. The Permian is overlain by the Comanche in most of the region.