ABSTRACT: The Capitan Massive (Reef) Facies, Permian Reef Geology Trail Guide, McKittrick Canyon, Guadalupe Mountains, West Texas & New Mexico

KIRKLAND, BRENDA, Louisiana State University, Baton Rouge, LA, and SUSAN A. LONGACRE and EMILY L. STOUDT, Texaco Exploration & Production Technology Department, Houston, TX

The Capitan Massive or "reef" facies is a prominent cliff-forming unit along the Permian Reef Geology Trail. The presence of the fusulinid Polydiexodina through part of the reef facies indicates that the Capitan Formation along most of the trail is age-equivalent to the middle and upper Yates Formation, hence older and stratigraphically below the Tansill-equivalent reef facies frequently visited in Walnut and Dark Canyons.

Modern reefs contain four dominant components: (1) a diverse framebuilding and binding community, (2) marine cement, (3) internal sediment that, along with marine cement, fills framework void spaces, and (4) bioeroding organisms. Similar distinctive elements are present in the Yates-equivalent Capitan Massive, except that evidence of bioerosion is rare. Framebuilding organisms are dominated, not by corals as in the modern, but by calcareous sponges and bryozoans. A number of binding organisms are also present. Volumetrically the most important of these encrusters is the red alga Archeolithoporella, which is associated with precipitation of prodigious amounts of marine botryoidal aragonite cement; a similar association of red algae and aragonite cement exists in modern reefs. Other pro inent binders/encrusters include the problematic organism Tubiphytes and various bryozoans. In addition to marine botryoidal aragonite cement, other marine cements include isopachous rims of Mg-calcite. Spectacular examples of layered, skeletal-derived and pelletal internal sediment fill framework voids and fractures throughout the Capitan Massive along the Permian Reef Geology Trail.

Carbonate cements are prominent features of the Capitan Massive. They record changing fluid chemistries from marine to meteoric to burial conditions. The most prominent cements include the following, listed in order from first to latest formed: (1) marine botryoidal aragonite fans; (2) marine isopachous fibrous calcite crusts; (3) marine inclusion-rich prismatic calcite crusts; (4) dolomite crystals precipitated on marine cements and calcspars; (5) fine to medium crystalline, luminescent, meteoric calcspar; (6) very coarsely crystalline, cloudy, luminescent, burial calcspar; and (7) medium to coarsely crystalline, dull luminescent, burial calcspar.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)