Chemostratigraphy of the Late Pleistocene to Holocene Transition In the Central Great Plains

Newly-derived, detailed numerical age control (¹⁴C & OSL) indicate that the Brady Soil of the Late Pleistocene to Holocene transition in the central Great Plains developed from about 14.5 to 10 ka. Notably, the Chronozone of the Younger Dryas (YD) climatic event (~12.9-11.6 ka) was coeval with only the middle of this major pedogenic interval. High-resolution stable C data (δ¹³C) from several profiles in the Wauneta study area of southwestern Nebraska were derived in an attempt to detect a YD signal, if such existed. Stable C analyses were conducted on total SOM, as well as on the fulvic acid, humin, and humic acid constituents. All lines of SOM isotope data exhibit a retardation of the emergence of the C₄ grassland during the YD event. Data from the various organic constituents mirror that of the total SOM signal, and, in some instances, further articulate and enhance the apparent impact of the YD climatic event. Because the Brady Soil was an upward building soil, organic C content also exhibits sensitivity to the YD, which was characterized by decreased organic C accumulation. This investigation demonstrates the utility of a detailed chemostratigraphic approach to deciphering the impact of the YD climatic event on progressive post-glacial development of the mixed and warm-season grasslands of the region.