Geochemical Characteristics of a Loess‐Soil Sequence in Central Kansas

Abstract

AbstractThis study focuses on a Barton County loess‐soil section in central Kansas in an attempt to retrieve the geochemical signature of the late Quaternary environmental change in the arid‐semiarid region and provide a data base of loess geochemical characteristics in the Great Plains. The data indicate that the elements (expressed as oxides) of the windborne fraction (<63 µm) that are easily solubilized and lost from the soil by chemical weathering and leaching are relatively sensitive to soil‐forming processes, whereas the insoluble elements of that fraction are controlled primarily by the chemical composition of the parent material. The geochemical imprint of pedogenesis superimposed on that of the loess parent material can be distinguished by comparing the magnetic susceptibility signature with the Fe2O3/Al2O3 ratio. Based on the geochemical imprint and radiometric dates (14C and thermoluminescence), the Bignell Loess (8000–5000 yr) is poorly weathered and the Brady Soil (10 000–8000 yr) is strongly weathered. The Peoria Loess (20 000–10 000 yr) has neither a traceable leaching nor weathering marker, and the Gilman Canyon pedocomplex (35 000–20 000 yr) is strongly leached. The reddish pedocomplex (70 000–35 000 yr) is the most strongly weathered, probably due to stable land surface conditions in a mild climate, and the Barton sand (92 000–70 000 yr) seems to have been subjected to a moderate weathering. Within the exposed portion of the Loveland Loess (260 000–92 000 yr), weathering indices are inversely correlated with the carbonate content and the carbonate‐rich soils were developed under warm dry environments before 92 000, around 193 000, and before 260 000 yr. The data also show that the geochemical background of Fe2O3 and Al2O3 is high in two portions of the section: from the Brady Soil to the Gilman Canyon pedocomplex and from LL1 to LL2 within the Loveland Loess. The geochemical background of Fe2O3 and Al2O3 in the loess‐soil sequence might have been dictated by that of eolian sources.