Radiocarbon dating limitations
During the Late Pleistocene, the sinkhole at Mammoth Site of Hot Springs formed when a cavern in the Minnelusa Limestone collapsed.This cavern collapse created a steep-sided sinkhole, that was about 65 feet (20 m) deep and 120 feet (37 m) by 150 feet (46 m) wide at the surface within a Pleistocene terrace underlain by Spearfish Shale.Mammoth bones were found at the site in 1974, and a museum and building enclosing the site were established.The museum now contains an extensive collection of mammoth remains.The presence of worm burrows and mammoth footprints found throughout these sediments, demonstrate that the laminated sediments within this sinkhole accumulated slowly and contemporaneously along the mammoth remains over a long period of time.Likely enticed by warm water and pond vegetation, mammoths entered the pond to eat, drink or bathe.Later, samples of the bone apatite (hydroxyapatite) fraction from mammoth bones were radiocarbon dated. Samples of bone apatite, which were not heat treated, yielded radiocarbon dates of 21,000±700, 25,640±320, and 26,075 975/-790 B. A single sample of bone carbonate was radiocarbon dated at 36,960±1170 B. The tooth plate yielded a uranium series date of 128,966 B. The results of the TL dating were apparently never published and preliminary OSL ages indicate that the sinkhole and its associated sediments and mammoth bones are indeed older than 26 ka.
Numerous attempts have been made to radiocarbon date these sediments.
Eventually the sinkhole filled, and the artesian spring diverted to the lower elevation of Fall River, as the river cut deeper in the valley floor.
Over thousands of years, the "hardened mud plug" inside the dried-up pond has remained stable.
The Mammoth Site of Hot Springs, South Dakota is a museum and paleontological site near Hot Springs, South Dakota.
It is an active paleontological excavation site at which research and excavations are continuing.