WHAT IS THE AEOLIAN RECORD REALLY TELLING US ABOUT THE LATE HOLOCENE OF THE CENTRAL GREAT PLAINS?

The stratigraphic records from dune fields and loess in the Central Great Plains (CGP), summarized by Miao et al. (2007), reveal a regionally coherent temporal pattern of Holocene aeolian activity: Rapid loess accumulation (~10-6 ka), followed by slow accumulation and soil development (~6-4 ka) and intermittent accumulation/soil development after ~4 ka, with an important interval of soil development around 2-1 ka and subsequent renewed accumulation in the Medieval Climatic Anomaly (MCA). Dune field OSL dating and soil stratigraphy provides a fuzzier picture, consistent with the loess record overall but emphasizing late Holocene activity, especially in the MCA. A closer look (and I have taken many close looks at the evidence over 20 years) brings out some interesting and potentially important complications. Weak soil development and young near-surface OSL ages in thick loess sections suggest relatively high accumulation rates from MCA almost to the present. The Nebraska Sand Hills dune field is marked by ubiquitous fresh-looking blowout complexes and minimal surface soil development (McKeehan, 2018), strongly suggesting a significant level of localized patchy reactivation that has affected much of the dune field (over the past few centuries?). Late Holocene dune OSL age distributions include many ages from outside the MCA or other well-defined intervals. All of these observations clearly cast doubt on a simple on-off model of the dune fields and local/regional dust sources, probably more evident in the late Holocene because of lower-amplitude climate variation and better preservation of the full geologic record. Xu et al. (2020) propose a kind of state-and-transition model for dune fields of northern China, with asynchronous local transitions between active and stable states because of feedbacks within the dune system and accidents of local site history, combining to produce regionally coherent response to climatic change, though with substantial fuzziness and hysteresis. A similar model could be applied to dunes and dust sources of the Central Great Plains.