AN ASSESSMENT OF ASH OCCURRING IN THREE COEVAL STALAGMITES FROM DeSoto CAVERNS, ALABAMA, USA
DeSoto Caverns, Alabama, USA, has been subjected to a long history of anthropogenic activities that includes burials by paleo-Native Americans, saltpeter mining, moonshining and its present transition into a show cave. Here, we report and assess the occurrence ash, clays and pollen associated with three coeval aragonitic speleothems whose age models are derived from 8 precise MC-ICP-MS, 230Th/234U radiometric dates.
Starting at 2030 years BP, a series of anomalous black laminations appear in all three of the studied DeSoto Caverns stalagmites and continue, with short interruptions, until collection in -58 BP. Petrographic investigations of thin sections reveal that the black laminations correspond to unconformities, whose durations vary between 25 and 225 years, and are predominately composed of ash.
The black laminated sequences typically begin with a rind of irregularly dissolved and truncated botryoidal aragonite bundles that are partially transformed into calcite. Upon this surface is the ash stained physical unconformity, followed by large competitively growing aragonite botryoides. This sequence reveals that the ash deposition is penecontemporaneous with a dissolution event, followed by a return to equilibrium cave conditions.
Two grains of Pinus (pine) and 10 grains of Poaceae (grass) pollen, ash from Arundinaria (common cane), ashes from yet unknown species and kaolinite have been identified in the black laminations. The absence of ash and other microdebitage preceding the start of human utilization of the cave at 2030 years BP, the paucity of pollen associated with the black laminations and the correlation of the unconformities to known and inferred periods of cave utilization suggest that the materials comprising the black laminations are sourced from the use of fire during periodic occupation of the cave by paleo-Native Americans.