New Mexico Geological Society Annual Spring Meeting — Abstracts

The lower Ordovician El Paso Formation contains four members, in ascending order: Hitt Canyon, Jose, McKelligon and Padre. The two sections studied, separated by an east-west distance of 175 km, are the Scenic Drive section (420 m) from the southern Franklin Mountains of west Texas and the Ram Gorge section (305 m) from the Big Hatchet Mountains of southwest New Mexico. Eighty-eight samples were collected at a 7.5-m interval for petrographic study to determine microfacies and, subseqriently, depositional environment. Both sections exhibit open circulation, shelf-facies depositional environments. Cross-laminated, sandy dolomite grades into wackestone/packstones and grainstones in the Hitt Canyon Member indicating a change of depositional environments from intertidal to subtidal. Allochems include echinoderms, trilobites, intraclasts, Nuia, gastropods, sponges, brachiopods, and cephalopods. Although the relative abundances differ, allochems are similar for each member with the exceptions of the Jose, which contains oolites and the Padre, which has ostracods and very few Nuia. The Jose Member consists of grainstones and lesser amounts of muds tbnes deposited in a shoaling enviroriment. Wackestone/packstones, boundstones and grainstones found in the McKelligon Member suggest that deposition took place in waters below normal wave base with channeled stromatolite and sponge mounds reaching the intertidal zone. The Padre Member is a cross-laminated, sandy dolomite at the base grading into wackestone packstones, boundstones, and grainstones near the top indicating that an intertidal, environment changed to one similar to that of the McKelligon Member.