Age and origin model for Fort Stanton Cave, New Mexico, USA

Fort Stanton Cave in central New Mexico, USA has all the appearances of a Mammoth-Cave-style epigene stream passage type of cave and not a hypogene cave like Carlsbad Cavern and Lechuguilla Cave. Its -72 km of passages are located in the Permian San Andres Formation between two small rivers fed by snow melt and rainfall on nearby Sierra Blanca, the highest mountain peak in the region, all of which are pertinent to Fort Stanton Cave's origin. Radiometric dates of vadose speleothems within the cave and a bedrock calcite vein narrow down the timing of speleogenesis. We measured a uranium-lead age of 12 My for the bedrock vein calcite, that speleogenesis of the Main Corridor has dissected, that provides a maximum age of the cave. The oldest vadose speleothems are >0.5 and <1 Ma, providing a minimum age for the cave. Using reasonable canyon incision rates for the two small rivers and these endmember age constraints, we show that Fort Stanton Cave is relatively young and that most of the cave likely formed 1 to 2 Ma. Cold water from Sierra Blanca and thicker soils/vegetation during glacial cycles of the Pleistocene provided conditions of cold CO2-charged groundwater with higher flow rates, the ingredients needed to form this large cave in soluble limestone units of the San Andres Formation.