COMBINED USE OF COSMOGENIC NUCLIDE, U-SERIES DISEQUILIBRIUM, PALEOMAGNETISM, AND OPTICALLY STIMULATED LUMINESCENCE WITHIN FITTON CAVE TO EVALUATE THE LANDSCAPE EVOLUTION OF THE BUFFALO NATIONAL RIVER, ARKANSAS (Invited Presentation)

Fitton Cave, within the Buffalo River watershed, is the largest known cave system in Arkansas with more than 12.8 km of mapped passages spanning 120 m in elevation range. It is formed within the Mississippian Boone Formation at the base of a structural trough bounded by two west-northwest-trending monoclines where perched water gathers above less-permeable Ordovician rocks. Four major cave levels are arranged in stacked, gently sloping phreatic tube or base-level passages separated by a few steeply inclined vadose passages. Several meters of coarse gravel and cobbles interbedded with fine sediments are deposited throughout the cave and are commonly capped with flowstone speleothems. To help understand the geomorphic history and landscape evolution of the watershed, we used cosmogenic nuclide, U-series disequilibrium, paleomagnetism, and OSL measurements to define the ages of sediment and speleothems within Fitton Cave.

Cosmogenic nuclide burial ages for coarse clastic material in higher passages suggest at least three phases of sediment aggradation at 2.2 ± 0.2 My, 1.3 ± 0.2 My, and 0.74 ± 0.16 My. Quartz OSL signals from the same sediments are saturated and thus broadly support these ages. Maximum U-series ages for flowstones overlying the clastic sediments provide minimum ages for the underlying deposits ranging from 400–700 ka and are consistent with cosmogenic dating results. Paleomagnetism results from fine sediment overlying the oldest basal gravel and cobbles dated by cosmogenic nuclides show normal polarity and suggest deposition during the Brunhes chron (<0.78 My) or Olduvai subchron (1.77-1.95 My).

The larger passages in Fitton Cave likely record periods of base-level stasis interrupted by periods of channel incision and water table lowering. The timing of sediment aggradation in Fitton Cave corresponds to climate changes associated with major advances of the Laurentide ice sheet several hundred km to the north. The results are in broad agreement with findings from other cave systems that are part of the larger Mississippi River drainage basin.