New Mexico Geological Society Annual Spring Meeting — Abstracts

The Lower Ordovician El Paso Formation, exposed in Hitt Canyon in the northern Franklin Mountains, can be stratigraphically and petrographically separated into four distinct members in ascending order, the Hitt Canyon, Jose, McKelligon and Padre. It is the purpose of this paper to determine the depositional environment of the four members of the El Paso Formation. Petrographic descriptions of forty-four thin sections, sampled at 7.5-meter intervals, indicate an open-marine to slightly restricted, tidal, platform-shelf depositional environment containing varied abundances of Nuia, trilobites, sponges, echinoderms, gastropods, cephalopods, Calathium, Pulchrilamina, and brachiopods. The grainstones and wackestone-packstones of the Hitt Canyon Member suggest intertidal to subtidal carbonate deposition at, or above normal wave base. The Jose member is characterized by a series of oolitic grainstones thereby indicating a shoaling environment. The abundance of sponge mounds and wackestones in the McKelligon Member suggests carbonate deposition in a subtidal wave base. The Padre Member
shows deposition of intertidal, cross-stratified, calcareous sandstones grading upward into subtidal wackestones deposited below normal wave base. Petrographic analysis of the El Paso Formation therefore indicates a general trend of fluctuating depth of deposition through the McKelligon Member. The Padre Member was then deposited as shallow, intertidal deposits grading into deeper, subtidal deposits.