A CHRONOSEQUENCE OF SOILS DEVELOPED IN EOLIAN SAND IN THE CENTRAL WISCONSIN SAND PLAIN

Following drainage of Glacial Lake Wisconsin, sediments on outwash fans and the lake bed were mobilized into a sandsheet with isolated low dunes and dune fields with large parabolic and transverse dunes. The large dunes formed at ca. 14-10.6 ka (Rawling et al. 2008, Geomorphology 100: 494), and are the youngest significant landscape disturbance. Older ages occur in the sandsheet and may represent a prior period of eolian activity. We described soil profiles at 19 sites in Adams County that have OSL age control on the underlying eolian sand; the soils form a maximum-age chronosequence of soils in sandsheet and dunes. Lab data include SOC, pH, Fe forms, detailed particle size analysis, and mineralogy by XRD. Morphologically, soils in dunes commonly have A/AB/Bw/C horizonation and sandsheet soils commonly have E horizons. Solum thickness on dunes of all ages is similar, while sandsheet profiles are thicker and have more genetic horizons. While variable, A horizon color is similar between groups; sandsheet A horizons are thicker but have less SOC. B horizons on dune crests are less red than B horizons in sandsheet. Except fines (<8 µm) and silt (8-50 µm) content of C horizons and K-feldspar in A horizons, no soil analytical properties show significant linear correlation with age of underlying sand. In dune soils, positive linear relationships exist between solum thickness and profile pH decrease, %SOC and silt content, and Fe forms and fines and silt. Negative linear relationships exist between pH and fines and silt content, pH and % SOC, pH and Fe forms, and pH and fines and silt. These relationships indicate that soil formation is driven by acidification and the content of fines and silt that provide surface area for weathering to produce Fe oxides and aid SOC storage. A strong, nearly 1:1, relationship between fines and silt content suggest they were added together and the fines are not a weathering product, although a weak relationship between age and K-feldspar of A horizons suggests weathering. The lack of time-dependent development of these soils is due to the low pedologic response potential (sensu Follmer 1986, Trans. 13th Int'l Cong. of Soil Science: 1112) of the quartz-rich sand; variations in the morphologic and analytical response appear to be controlled by processes responsible for acidification and deposition of fines and silt.