Abstract

Middle Permian (Guadalupian) strata in the Apache Mountains of West Texas contain a well exposed surface portion of the Capitan Reef in canyons that cut through the northern escarpment in the eastern part of the mountains. In Panther Canyon, the massive part of the Capitan Reef is well exposed and overlain by a stratigraphic sequence of lagoonal carbonate deposits herein referred to the Yates and Tansill Formations. The presence of these two back-reef Guadalupian units in the Apache Mountains area has been suggested but never precisely documented by faunal and lithologic evidence. At the entrance to Panther Canyon, two sections of these stratified carbonate rocks have been measured and described: the PC7 section, 31.8 meters thick, contains eight “packages” of distinctive carbonate lithofacies and the PC8 section, 86 meters thick, contains 18 such “packages”. Faunal assemblages consisting of algae, sponges, brachiopods, ostra-codes, bryozoans, and foraminifers, are Capitanian (late Guadalupian) in age. Fusulinids present are Codonofusiella extensa, Yabeina texana, Paradoxiella pratti, and Reichelina lamarensis. The ranges of these genera enable these sections to be biostratigraphically correlated to extensively studied sections in the nearby Guadalupe Mountains to the north. Furthermore, these genera have never been reported from the area of this study and only recently have been reported from late Guadalupian debris deposits in the northwestern part of the Apache Mountains along with the youngest Guadalupian fusulinid Paraboultonia splendens.

Microfacies analysis of the carbonate rocks of these “packages” has revealed the stratified carbonate rocks were generated within reef, proximal back-reef, and lagoonal depositional environments controlled by the eustatic conditions during the time of deposition. Lagoonal rocks appear to contain two distinct microfacies: (1) Biomicrite containing dasycladacean green algal remains deposited on the lagoonal floor in calm, marine water. A barrier reef would disrupt any wave action and protect the lagoon allowing for the deposition of fine carbonate mud amongst the skeletal remains of the lagoonal inhabitants. (2) Bioclastic intrasparite deposited in barrier wash-over fans generated by storm events. Large, storm generated, high energy waves could wash over the barrier reef and disturb the fine carbonate lagoonal sediment and transport it out of the barrier inlets. Reef detritus generated by wave action can mechanically erode the fore-reef structure and be transported shoreward and deposited within the lagoon. The resultant allochemical composition of the rocks would be fore-reef derived carbonate intraclasts amongst lagoonal faunal and floral components.