Proposed age and origin of gypsum needles of Crystal Crawl, Fort Stanton Cave, New Mexico
Victor J. Polyak, Donald G. Davis, Paula P. Provencio, and Yemane Asmerom
Crystal Crawl in Fort Stanton Cave near Capitan, New Mexico, was once covered with a forest of gypsum needles that has been almost entirely destroyed by over 100 years of frequent visitation and mineral collection. One of those needles was sketched and added to the Great Divide expedition report in 1891. We studied needles from three collections and noted regular-looking growth banding in many of them. The average band width of 10 measured needles (0.16 to 0.38 mm/ band) is similar to growth rates of gypsum needles previously published (0.07 to 0.21 mm/year), supporting our interpretation that the banding was produced from annual growth of the gypsum needle. With that interpretation, we estimate that the individual needles of Crystal Crawl took 100 to 500 years to grow. We also measured the age of one needle based on two uranium-series analyses of needle 2 (3.3 ±2.7 and 4.3 ±3.9 ka) that show that it grew during the Middle or Late Holocene. Our interpretation is that the entire crystal forest grew during this time. It is likely that the needle forest grew during a time when the cave environment shifted to slightly more evaporative conditions, which could have been during onset of drier Early and Middle Holocene climate, or initiated due to collapse which created the large entrance of Fort Stanton Cave. Alternatively, the needles could have grown following mobilization of gypsum by the last flooding of the cave that reached the Crystal Crawl floor level. This suggested Holocene age and origin for the gypsum forest is also evidence that could support a similar hypothesis for deposition of the Snowy River calcite, also in Fort Stanton Cave.
- Polyak, Victor J.; Davis, Donald G.; Provencio, Paula P.; Asmerom, Yemane, 2014, Proposed age and origin of gypsum needles of Crystal Crawl, Fort Stanton Cave, New Mexico, in: Geology of the Sacramento Mountains region, Rawling, Geoffrey; McLemore, Virginia T.; Timmons, Stacy; Dunbar, Nelia, New Mexico Geological Society, Guidebook, 65th Field Conference, pp. 157-162.