A TWO-MILLION YEAR RECORD OF CLIMATE DRIVEN CAVE-SEDIMENT AGGRADATION AND VALLEY INCISION IN THE SOUTHERN OZARK PLATEAUS: A MULTIPLE GEOCHRONOMETER STUDY OF FITTON CAVE, NORTHERN ARKANSAS

To help understand the history of the cave formation and landscape evolution in the southern Ozark Plateaus region, multiple geochronometers were used to constrain ages of deposits in upper-level passages of Fitton Cave, formed in the Cecil Creek catchment adjacent to the Buffalo River in northern Arkansas. These constraints demonstrate an early Pleistocene period of passage formation and cave-sediment aggradation followed by passage incision after 0.75 Ma. Cosmogenic nuclide burial dates mark pulses of coarse cobbles into the cave at 2.2 ± 0.2 Ma (n =2 sites) as well as slightly higher gravels at 1.25 ± 0.2 Ma (n = 3 sites). In support of these dates, finer grained sediments within and above these two coarse horizons carry dominantly reversed-polarity magnetization (ages > 0.79 Ma) and yield thermally transferred optically stimulated luminescence (TT-OSL) dates of 1.24 ± 0.09 Ma, 0.96 ± 0.06 Ma, and saturated but > 0.74 Ma. A start of passage incision is constrained by a third pulse of coarse sediment with a cosmogenic date of 0.74 ± 0.16 Ma and a TT-OSL date of 0.73 ± 0.05 Ma deposited in a small passage incised about 3 m below an older sediment interval. Maximum U-series disequilibrium dates for flowstones that cap the clastic sediments at several locations range from 0.7 to 0.4 Ma, providing minimum ages for the stabilization of underlying sediments. U-series dates from several stalagmites range from 0.42 to 0.17 Ma, indicating that vadose zone conditions persisted in upper-level passages during ~23 m of water-table lowering as the adjacent Cecil Creek valley incised.

Coarse sediments washed into Fitton Cave at 2.20, 1.25, and 0.74 Ma have ages equivalent to Laurentide glacial tills at their southern extent in northern Missouri (Balco and Rovey, 2010). This suggests a climate control on cave-sediment aggradation, perhaps by increased periglacial sediment production, vegetation change, or variable hydrologic flow. Compared to a modern water table projection from the cave outlet spring, the post-0.75 Ma rate for the Cecil Creek valley incision is ~31 m/Ma.

Balco and Rovey, 2010, Geology, 38, 795-798