Structural and Facies Control of Hypogenic Karst Development in the Guadalupe Mountains, New Mexico

The Guadalupe Mountains are the exhumed remnants of a Permian reef complex uplifted beginning around 21 million years ago. The caves of the Guadalupe Mountains were formed by the mixing of deep-circulating meteoric water and hydrogen-sulfide-rich brine derived from surrounding oil and gas deposits. Cave development is controlled by fracture zones, faults, and structures associated with Permian and Tertiary tectonics. Local passage character can be affected by changes in facies and lithology.

The overall pattern of cave development shows strong linear trends that are correlative to linear features seen in aerial photographs and geologic maps. These features are consistent with broader structural trends in the Guadalupe Mountains and reflect fracturing, faulting, and folding during uplift. Some anticlinal features reflect deposition of Permian sediments across syndepositional faults. Many of these syndepositional faults can be observed in the caves and exhibit a strong influence on both overall passage trends and on passage character.

There are large breccia zones associated with syndepositional faults. In these areas, cave passages typically change from large, linear trunk passages to complex three-dimensional mazes of smaller passages. Forereef deposits, paleokarst, and paleochannels through the reef can also be preserved as breccia zones and have a similar effect on passage character.

While overall speleogenesis crossed formational boundaries, lithology had some influence on passage character. The backreef units contain more rectilinear maze-type passages than the underlying reef and forereef units, probably reflecting more tightly-spaced fracturing and greater porosity. Large trunk passage development is prevalent in the Capitan formation, especially along the reef/forereef transition. Other facies changes exhibit significant, but more localized controls on passage character. In some backreef units, Permian tepee structures control the shape and orientation of some cave passages. Variations in reef facies, cementation, and dolomitization may also exhibit some localized influence on passage character.