CALIBRATION OF RADIOCARBON AGES ON LATE HOLOCENE PALEOSOLS TO CONSTRAIN THE GEOMORPHIC EVOLUTION OF THE WHITE RIVER BADLANDS

The intent of this research was to link geomorphologic landscape evolution with climate change in the White River badlands. Sod tables containing late Holocene Paleosols were sampled for radiocarbon (¹⁴C) dating of bulk humate. The paleosols formed during intervals of conducive climate and landscape stability. Subsequent incision cut across the paleosols, forming sod tables as remnants of dissected pediments. The ¹⁴C samples received from lab were calibrated by creating a normal distribution curve of beta particles per each sample, with one unit of standard deviation. The normal distribution curve was then placed on the Y-axis of a dendrochronology graph. A dendrochronology graph relates raw ¹⁴C sample dates in beta particles to Calendric years based off ¹⁴C data gathered from tree rings. Two parallel lines were drawn using one unit of standard deviation horizontally to intersect the dendrochronology graph at the two points. At the intersection of the two horizontal lines and the dendrochronology graph, two vertical lines were drawn down to indicate age in calendar years. The calibrated dates range from 74 ± 198 AD to 1360 ± 49 AD with the majority of the dates residing between 900–1350 AD, in the range of the Medieval Climate Anomaly (MCA). We began this research to investigate if the MCA appeared to cause the incision event, but are now open to the possibility that the Little Ice Age (LIA, 1500 AD – 1850 AD) may have been the trigger. To assist in identifying whether the dissection of slopes occurred in association with the MCA or the LIA, we turned to another geomorphic system - dunes, and our ages determined for their activity strongly suggest landscape disruption by the LIA.