BONE DISTRIBUTION AND DIAGENETIC MODIFICATIONS AT THE MAMMOTH SITE OF HOT SPRINGS, SOUTH DAKOTA, USA

The Mammoth Site of Hot Springs, South Dakota, is the largest primary accumulation of mammoth remains in the new world. The accumulation and preservation of mammoth remains was accomplished in the form of a karst depression (sinkhole) containing a spring fed pond. The Mammoth Site sinkhole formed approximately 26,000 years ago when a cavern in the Minnelusa Formation collapsed and developed a breccia pipe. The overlying strata is the Permian-Triassic Spearfish Formation, which also caved in. This opening is an elliptical configuration measuring 37 m X 46 m and has been drilled to a depth of 20 m without reaching the bottom of the Pleistocene deposit. Artesian water issuing principally from one identified spring conduit introduced a warm pool environment and maintained an energy gradient that affected sediment dispersal. The sinkhole fill consists of laminated sediments ranging from clay to coarse sand. The environment of the deposits and the nature of the sediments being deposited have preserved even the most delicate bones, such as mammoth hyoid elements. The bones of vertebrates and invertebrates at the Mammoth Site are not permineralized. The warm spring waters that infiltrated the sinkhole leached out the collagen in the bones. The presence of spiral fractures occurs on a small number of mammoth bones, providing additional data on the taphonomy at the Site.

We present the bone distribution pattern in the bonebed and discuss diagenetic modifications at this unique and complex setting.