The Sangamon paleosol in and adjacent to the Lower Mississippi Valley

Age, compositional, pedological, and stratigraphic data indicate that at most localities the “red” paleosol in the northern part of the Lower Mississippi Valley (LMV), from Illinois to western Mississippi, is the Sangamon paleosol (SP) as recognized from Iowa to Ohio and Minnesota to southern Illinois. The SP is best developed in the upper part of the 190-120 ka Loveland loess, present on ridges, high bluffs, and terraces within and adjacent to the LMV. Thermoluminescence and isotopic age data indicate that at any given locality the SP can represent all or part of marine isotope stage 5, from about 130-55 ka. Soil color, structure, chemistry, mineralogy, and correlation with ice-core oxygen-isotope curves suggest that the SP formed when the regional midcontinent climate was warm to hot with seasonal or longer periods of drought. Unconformable relations within the SP, and between the SP and overlying and/or underlying soil/sediment, suggest that in the LMV the patchwork of relict SP sections encompasses several periods of erosion and soil formation within marine isotope stage 5. Regional pedologic data also suggest that down-valley (southward) trends in temperature and precipitation were similar to the present: temperature and precipitation increase; seasonality, and variation in annual to decadal precipitation, decrease.