STRATIGRAPHY, SEDIMENTOLOGY, AND STRUCTURAL GEOLOGY OF GYPSUM CAVES IN EAST CENTRAL NEW-MEXICO

Hundreds of solution caves have developed in evaporites and carbonates of the Permian San Andres Formation where it crops out between Vaughn and Roswell, New Mexico, USA. Several of the caves are over 3.2 km (2 miles) in length, and the deepest has a vertical extent of over 120 m (400 feet). These gypsum caves afford an extraordinary opportunity to examine the evaporite rocks in which they are developed. We have exam ined interbedded gypsum and dolostone strata exposed in the walls of 1 1 of these caves, and show stratigraphic sections on two geologic cros s sections. Gypsum textures exposed in the caves include massive, nodu lar, and laminar types. While we refer to them as ''gypsum caves,'' gy psum is not the only lithology exposed. Some cave passages and rooms a re developed in thick dolostone units intercalated with or overlain by gypsum beds. Correlation of beds exposed in two or more caves has all owed us to infer the local geologic structure. The sedimentary sequenc e penetrated by a cave exerts a profound effect on the geometry and pa ssage cross-section of the cave. Many cave passages have gypsum walls and a dolostone or limestone floor. Although many of the cave passages flood completely during major storm events, the stairstep profile of most of the caves is indicative of speleogenesis that has occurred pre dominantly within the vadose zone.