Abstract The first part of the day covers Precambrian stratigraphy and industrial mineral deposits in the Van Horn area. The Tumbledown Mountain talc deposit is situated on the northwestern flank of Beach Mountain, both of which are located a few miles north of Van Horn. The Milwhite talc deposit is reached by an unpaved road that traverses Red Valley and Hackberry Creek and crosses the Van Horn Sandstone, Hazel and Allamoore formations. In addition to the talc deposit in the Allamoore Formation, the complex structures in Tumbledown Mountain can also be observed. The lower Paleozoic Bliss, El Paso and Montoya Formation, and the Permian Hueco Limestone are well exposed in adjacent escarpments and fault blocks in this area. Thereafter, a visit will be made to the Texas Architectural Aggregate underground brucitic marble mine at Marble Canyon in the Sierra Diablo. The route is then retraced to Van Horn and the second part of the day is spent traveling westward on 1-1 o. Stops will be made at the Precambrian Carrizo Mountain Group, GiffordHill road metal quarry and Hillside fault, the type locality of the Texas Lineament. Further to the west a stop will be made at the Pioneer-Apache talc plant, and also to discuss the inactive fluorite deposits located to the south in the Eagle Mountains. Further to the west-northwest, along 1-1 0, the route crosses Eagle Flat and a final stop will be made to view the Sierra Blanca rhyolitic laccoliths and contained beryllium prospect. To the south of this locality is the Quitman Mountains, ring dike and intra-cauldron volcanic pile. The final part of the excursion route follows the Rio Grande Valley in a northwesterly direction to El Paso.

Abstract This study evaluates the role of compaction-induced differential subsidence as a control on carbonate-platform architecture, sequence development, and early diagenesis in Permian strata of the Delaware and Midland basins, west Texas and southeast New Mexico. The geometry and stratal patterns of compaction-modified sequences identified from outcrops in the Sierra Diablo, Guadalupe, and Brokeoff Mountains are comparable to those observed in seismic lines from the Northwest and Eastern shelf areas. The modification of platform geometries by differential compaction varies spatially and temporally in the studied area and is most important where Leonardian and Guadalupian highstand strata (sequences and sequence sets) have prograded over antecedent aggradational and/or erosional platform margins and wedge-shaped packages of compactible basin facies. A "compaction hinge" delineates two mechanically distinct parts of a carbonate platform with contrasting stratal patterns, facies, and accommodation histories. The hinge normally develops in highstand strata deformed by compaction-induced differential subsidence over a preexisting platform margin. Updip of the compaction hinge, platform topsets are generally parallel and of constant thickness, whereas downdip, the same topsets thicken, dip, and diverge basinward toward a downward-deflected depositional platform margin. The alteration of platform architecture by differential compaction during a sea-level lowstand forms a compaction-modified sequence boundary. During a lowstand, flexural deformation driven by compaction-induced differential subsidence (at an outcrop-constrained average rate of 0.19 m/k.y.) modifies platform-top physiography and can generate relief and fractures to control facies patterns, stacking patterns, and the distribution of penetrative paleokarst. The resulting compaction-modified platform architectures and sequence boundaries show a characteristic suite of features that allows their identification using the criteria presented herein. The progressive further steepening of the dips formed across compaction-modified sequence boundaries during burial aids their recognition in outcrops and especially on regional seismic lines. The control of compaction-induced differential subsidence on carbonate-platform development has previously been underestimated. Differential compaction can significantly modify the development and dynamics of carbonate platforms and holds important implications for the interpretation of stacking patterns, platform architecture, paleoecology, diagenesis, and accommodation history.

INTRODUCTION AND ACKNOWLEDGMENTS The strata of the Guadalupe Mountain region can be regarded as the classic Permian of North America. Over 80 years ago these rocks and their fossils were described in some detail, and the first comprehensive report on the marine Permian faunas of North America was based on specimens from the Guadalupe and the Delaware mountains. Furthermore, recent stratigraphic studies in this area have shown that the strata there are particularly significant; as they are transitional in nature, they enable us to correlate the typical marine fossiliferous Permian of the Southwest with contemporaneous beds that are nonfossiliferous. It is the purpose of this report to achieve an understanding of the ammonoid faunas of the Guadalupe Mountain area and to compare and relate these faunas with those found in the well-known Glass Mountain sequence. Naturally, it is impossible to ascertain the full significance of any fauna by a study of specimens from a limited area, and the writers have therefore attempted to take advantage of the rather extensive collections at their disposal. All the Permian ammonoids that have resulted from the recent work of the United States Geological Survey in the Guadalupe Mountain area have been made available to the writers. Also, they have very large collections from the Glass Mountains, which add appreciably to the number of species known from there, and smaller collections from the Sierra Diablo and the Hueco, Finlay, and Chinati mountains of west Texas and from various localities in north-central Texas. . . .