Day 3 Field Stops

Abstract

Abstract Numerous caves are present in the Guadalupe Mountains, with Carlsbad Cavern and Lechuguilla Cave being the most spectacular (Figure 32). The theories of local cave formation have changed over the last 50 years. Dissolution was initially attributed to “normal cave processes” of carbonic acid occurring in rainwater (Bretz, 1949). During the last 20 years, a more complex model has evolved for development of caverns in the Capitan system (Jagnow, 1979, 1989; Hill, 1989, 2000; DuChene and McLean, 1989). Based on cave geometries and the geochemistry of the cave fill, Hill (1987, 1995, 1996, and 2000) postulated four stages of cave development. The last and volumetrically most important dissolution event was “sulfuric acid karst” associated with basinal hydrogen sulfide mixing with oxidizing freshwater during the last 15 million years (Figure 33). This model has been substantiated and is now being considered for other cave systems around the world. The Carlsbad Caverns Visitor Center is situated directly above the Capitan reef and along what is termed the Reef anticline (Figure 34). The cavern is developed primarily along a series of joints that are parallel or perpendicular to the reef front. Passages are confined to the limestone reef, being sandwiched between backreef and forereef deposits. The natural entrance to the cavern (Figure 35) is a paleospring developed in the Tansill formation. According to the work of Hill (1987), the entrance paleospring was operative ~1 Ma ago, but had ceased