Possible sources of extractable Na (water‐soluble plus exchangeable) considered for Illinois solonetzic soils were: Pennsylvanian bedrock, Illinoian till, Farmdale and Peorian loess, and ocean spray salts from rain. Extractable Na in Illinois sononetzic soils originated chiefly from the weathering in situ of Na‐rich feldspars of the parent loess. Members of the albite series (namely, albite and oligoclase) and the Na‐rich microcline, anorthoclase, aggregate 70 to 80% of the silt‐sized Na‐bearing minerals which comprise 75 to 90% of the total mineral Na in these soils. Sufficient Na has weathered from the 50 to 5µ silt fraction in solonetzic soils to account for accumulations of extractable Na currently present in their B horizons. Little evidence of local variability in loess or differential weathering between solonetzic and associated soils suggests that differential redistribution of soluble products of weathering is responsible for extractable Na accumulations in Illinois solonetzic soils. It is believed that the local distribution of solonetzic soils is correlated with more permeable till zones of the highly impervious, underlying Illinoian till paleosol. Based on this assumption, a redistribution mechanism involving aqueous movement and differential segregation of soluble products of weathering is presented.
Loess thickness and particle size changes along six Peoria loess traverses in Illinois and southwestern Indiana were investigated by fitting the data to various mathematical models by computer. An exponential model, a logarithmic model, a power function, and an additive exponential model developed in this study were tested. The decrease in mean particle size, which is due to changes in the coarse silt content, both windward and leeward from the source is explained best by the additive exponential model. Mean particle size changes much more rapidly near the source than afar.Leeward of the source, two changes in the rate of loess thinning occurred. The change closest to the bluff is related to particle size differences with distance from the source. The second change is attributed to greater loess deposition in a wider zone near the source by winds from different directions. Windward of the source, no change in the rate of loess thinning due to particle size differences was observed.Based upon the particle size and thickness data presented, the decrease in loess thickness from its source is explained best by an additive exponential model. Leeward of the source where two changes in the rate of loess thinning occur, three exponential terms are needed to accurately characterize loess thickness. The decrease in loess thickness with distance from the source which is due to the more rapid decrease in particle size near the source is defined by the first exponential term. The decrease in loess thickness associated with deposition by winds of different directions is described by the second exponential term. The third exponential term depicts the regional loess thinning due to a decrease in the number of loess particles with distance from the source. Windward of the source only two exponential terms are needed to accurately describe loess thickness because no change in the rate of loess thinning due to particle size differences was observed.
Total loess (predominantly Peorian loess) thickness in southeastern Illinois and southwestern Indiana ranged from somewhat less than 40 inches to more than 300 inches, and the thinning rate of the loess was a linear function of the logarithm of the distance from the source. Peorian loess was present throughout the area, but Farmdale loess was present in significant amounts only in extreme southern Illinois and in extreme southwestern Indiana. Loveland loess was present sporadically beyond the limit of Illinoian glaciation. In the Wabash basin, loess thickens to the south as the valley becomes wider, the loess‐receiving landscapes become older, and the sediments in the valley become more silty. West‐northwest winds were important in the loess deposition of this region, but deposition of loess by easterly and southwesterly winds in the lower Wabash and Ohio river basins was shown to be more important than has been previously noted.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.