A Chronotoposequence of Soils Developed in Loess in Central Louisiana

Abstract

AbstractSurface soils developed in Sicily Island loess (thermoluminescence age 75 000–95 000 yr B.P.) and Peoria loess (thermoluminescence and 14C age 9000–22 000 yr B.P.) were sampled to study a chronosequence in the lower Mississippi River valley. A toposequence composed of an Udalf and an Aqualf was sampled in each of the loesses to evaluate relationships between topography and soil formation. Morphological, physical, chemical, and mineralogical properties were examined to determine the influence of time and topography on soil formation. Soils developed in the older Sicily Island loess had thicker argillic horizons and sola, a greater degree of horizonation, and greater maximum and total sola clay contents than younger Peoria loess‐derived pedons. Chemically, soils developed in the older loess had less exchangeable Ca, more exchangeable Al, lower mean effective cation exchange capacity (ECEC) per unit clay for the whole argillic horizon, lower base saturations, and were more acidic than their younger counterparts. Kaolinite and vermiculite were more abundant in the older Sicily Island loess‐derived soils while smectite and mica percentages were higher in Peoria loess‐derived pedons. Topography influenced soil formation through differences in soil drainage conditions. Soils occupying better‐drained sites had thicker sola and argillic horizons, thinner total surface (A + E) horizons, redder hues, and were more acidic with less exchangeable Ca, lower base saturations, and lower mean ECEC per unit clay for the whole argillic horizon than soils forming under poorly drained conditions. Kaolinite and mica were more abundant in the better‐drained soils while smectite was in greater quantities at the poorly drained sites.