Position of San Andres Group West Texas and New Mexico

Abstract

Stereograms were made of a wide area of the South Permian basin to gain a regional perspective of the upper Permian stratigraphy. Recognized as major structural features are the Val Verde basin, Fort Lancaster platform, Blackstone arch, Cerf basin, San Simon syncline, and Halfway syncline. Structural features were controlling factors in Permian deposition and the stratigraphic phenomena of the Permian basin are related directly to lateral gradation. Surface studies and subsurface work reveal that, as a result of this gradation, many of the various facies are time equivalents. Unconformities are recognized as the best time markers because of the changing facies. Surface trace reveals that several hundred feet of Word clastics grade into the Vidrio limestone in the northeas ern Glass Mountains. Consequently the Vidrio is recognized as the upper division of the Word and the Capitan formation is restricted to the reef facies of the Gilliam to conform with its usage in the Guadalupe Mountains. It is proposed to place the base of the Word at a conglomerate about 300 feet below the present base of the formation. In the Glass Mountains, evidence suggests the pre-Whitehorse unconformity at the base of the Gilliam, and the unconformity at the base of the Word is believed to be equivalent to the unconformity at the base of the El Reno. The San Andres group is believed by the writer to be the time equivalent of the Word formation, the lower two divisions of the Delaware Mountain group, and the El Reno group, each of which is separable into an upper and lower division over a wide area in the South Permian basin. These correlations are supplemented by paleontologic information which shows that preponderance of evidence is accumulating that the San Andres group should be placed in the Guadalupe series instead of the Leonard series.