The fossil pearls of the Million-Pearls Flowstone, Fairgrounds Room, Fort Stanton Cave, New Mexico USA

Authors

• Victor J. Polyak, University of New Mexico, USAFollow
• Paula P. Provencio, University of New Mexico, USAFollow
• Yemane Asmerom, University of New Mexico, USAFollow

Highlights

• Two cave pearl layers are preserved in a thin flowstone on an extinct stream bed
• The pearls are referred to as ‘fossil pearls’ due to their unusual occurrence
• The pearls consist of calcite and exhibit layers of white amorphous-like silicate material
• Their nuclei are composed of aggregates of calcite crystals or clay balls
• Timing of the pearl layers are coeval with two Last Glacial stadials

Abstract

‘Fossil’ cave pearls in the Fairgrounds Room of Fort Stanton Cave form two distinct layers in a flowstone sample, FS-14-2. The flowstone in the Fairgrounds Room covers a mud-silt bank and the extinct streambed that extends across the room. Uranium-series dates of two pieces of flowstone from this room, one piece from the higher end of the flowstone (FS-14-1, devoid of pearls), and another piece from the lower end of the flowstone (FS-14-2, rich in pearls), show that the flowstone was deposited during the Last Glacial period (60,000 to 11,000 yr BP).  The two cave-pearl layers in FS-14-2 yielded U-series ages of 31,132 ± 305 and 31,682 ± 608 yr BP for the older layer and 26,441 ± 295 yr BP for the younger layer.  A uranium-series date on the thin layer of gypsum that coats the flowstone shows that the gypsum was deposited during the warmer and effectively drier later Holocene. The cave pearls formed along the lower extent of the flowstone in a flat cave-floor setting suitable for cave pearl formation. A vast majority of the pearls are restricted to two layers, which seems to suggest that climate was the driver, where wetter-than-normal glacial climate ~31,500 and ~26,700 yr BP resulted in increased dripping from the ceiling and greater water flow and flow variability on the flowstone.  Cave pearl growth coincides with Glacial Stadials GS-5.2 and GS-3, respectively, suggesting that the glacial stadials delivered greater effective moisture to the region.

DOI

https://doi.org/10.5038/1827-806X.ijs2605

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Recommended Citation

Polyak, V.J., Provencio, P., Asmerom, Y., 2026. The fossil pearls of the Million-Pearls Flowstone, Fairgrounds Room, Fort Stanton Cave, New Mexico (USA). International Journal of Speleology, 55(3), ijs2605 https://doi.org/10.5038/1827-806X.ijs2605