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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 22 (1938)

Issue: 12. (December)

First Page: 1704

Last Page: 1705

Title: Paleozoic Stratigraphy of the Franklin Mountains of West Texas: ABSTRACT

Author(s): L. A. Nelson

Article Type: Meeting abstract

Abstract:

The Franklin Mountains are located 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 meridian to a point about 4 miles north of the Texas-New Mexico boundary line.

The Franklin Mountains are eroded block mountains typical of the basin-and-range structure of the southwestern United States. The west side is a steep dip slope developed principally on beds of limestone. The east side is a fault scarp.

The Paleozoic stratigraphic section, which aggregates 5,600-7,000 feet in thickness, is as follows: Permian, Wolfcamp formation; Pennsylvanian, Magdalena formation; Mississippian, Helms formation; Devonian, Canutillo formation; Silurian, Fusselman limestone; Ordovician, Montoya and El Paso limestones; Cambrian, Bliss sandstone. The section is overlain by the Comanche and rests, in places, on pre-Cambrian granite and at other places on the Llanoria quartzite.

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The exposed portion of the Magdalena formation consists primarily of thin-bedded, light gray to black limestone, and for convenience it is divided into the following three units: the La Tuna at the base, the Berino, and the Bishop's Cap at the top.

Comparatively few fossils have been reported from the near-by localities; hence it is difficult to use them to correlate the Magdalena of the Franklin Mountains with formations in these areas. A few closely allied genera and species of gastropods and brachiopods are reported from the Taos region of northern New Mexico and from the McCoy region and the Mosquito Range of Colorado. However, the most striking similarity is to a gastropod fauna described from the St. Louis outlier of Missouri and the equivalent St. David's limestone of Illinois.

The Permian is represented by about 650 feet of exposed sediments known as the Wolfcamp. These sediments occur as outliers some distance west of the Franklin Range and are separated from the exposed Magdalena sediments by alluvial deposits; hence the contact between the Magdalena and the Wolfcamp has not been seen.

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