Caves exist in the Capitan Formation in the Guadalupe, Apache, and Glass Mountains, southeastern New Mexico and West Texas. Four episodes of karsting have been identified in the Guadalupe Mountains: (1) Stage 1 fissure karst (Late Permian), (2) Stage 2 spongework karst (Mesozoic), (3) Stage 3 thermal karst (Miocene), and (4) Stage 4 sulfuric acid karst (late Miocene to present). The last sulfuric acid episode was responsible for the large cave passages and for the distinctive deposits within these caves (gypsum blocks; native sulfur; the pH-indicator minerals endeliite, alunite, and natroaiunite; and the uranium minerals tyuyamunite and metatyuyamunite). The hydrogen sulfide responsible for forming sulfuric acid in the Capitan reef originated from hydrocarbons in the Delaware Basin. Stage 4 caves in the Glass Mountains are also of sulfuric acid origin, showing that the basin probably degassed hydrogen sulfide around its entire margin. Caves also exist in the subsurface Capitan on the eastern and northern sides of the Delaware Basin. San Simon Swale/Sink on the east and breccia pipes/domes on the north may stope down to the cavernous Capitan. The same sulfuric acid mechanism that formed caves in the exposed Capitan may have also been partly responsible for caves in the subsurface Capitan.
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The Capitan Formation of southeast New Mexico and west Texas contains one of the world's best exposed and most famous reefs. Depositional and diagenetic models derived from the Capitan have been used to interpret carbonate strata throughout the world. This volume contains 12 state-of the- art papers summarizing major new research on the Capitan, putting the Capitan into a modern statrigraphic, depositional, paleontologic, and diagenetic framework.