Impact of Climate and Parent Material on Chemical Weathering in Loess‐derived Soils of the Mississippi River Valley

Abstract

Peoria Loess‐derived soils on uplands east of the Mississippi River valley were studied from Louisiana to Iowa, along a south‐to‐north gradient of decreasing precipitation and temperature. Major element analyses of deep loess in Mississippi and Illinois show that the composition of the parent material is similar in the northern and southern parts of the valley. We hypothesized that in the warmer, wetter parts of the transect, mineral weathering should be greater than in the cooler, drier parts of the transect. Profile average values of CaO/TiO2, MgO/TiO2, K2O/TiO2 and Na2O/TiO2, Sr/Zr, Ba/Zr, and Rb/Zr represent proxies for depletion of loess minerals such as calcite, dolomite, hornblende, mica, and plagioclase. All ratios show increases from south to north, supporting the hypothesis of greater chemical weathering in the southern part of the valley. An unexpected result is that profile average values of Al2O3/TiO2 and Fe2O3/TiO2 (proxies for the relative abundance of clay minerals) show increases from south to north. This finding, while contrary to the evidence of greater chemical weathering in the southern part of the transect, is consistent with an earlier study which showed higher clay contents in Bt horizons of loess‐derived soils in the northern part of the transect. We hypothesize that soils in the northern part of the valley received fine‐grained loess from sources to the west of the Mississippi River valley either late in the last glacial period, during the Holocene or both. In contrast, soils in the southern part of the valley were unaffected by such additions.

Rates of consumption of atmospheric CO<sub>2</sub> through the weathering of loess during the next 100 yr of climate change

“…The model was also consistent with a small amount of dolomite at depth in pedons 9, 17, 20-22. Consistent with this, other researchers have observed dolomite in deep loess samples near pedons 21 and 22 (Ruhe, 1984;Pye and Johnson, 1988;Muhs et al, 2001). To ascertain definitively if dolomite was present in any of these more southern profiles, we attempted to get samples in collaboration with D. Muhs (US Geological Survey).…”

“…In our previous study , we relied on published chemical analyses and X-ray diffraction data for the Peoria loess sampled from pedons along the Mississippi transect (Muhs et al, 2001). Williams et al (2010) also reported new quantitative X-ray diffraction (XRD) analyses of Muhs' samples from pedons 1 (Clayton County, IL), 13 (Lauderdale County, TN), and 22 (St. Francisville, LA).…”

“…The mineral model included montmorillonite, illite, plagioclase, potassium feldspar, quartz, dolomite, and kaolinite plus minor calcite, chlorite, ferrihydrite. Using this mineral model, we calculated the mineralogy of the bulk elemental data from Muhs et al (2001) for all the pedons along the north-south transect. Based on these calculations, the extent of depletion of plagioclase feldspar along the transect was observed to increase from north to south .…”

The influence of litho- and pedogenic processes on Luvisols formation of selected area of Vistula glaciation

“…The re sults obtained were ver i fied based on the Till-3 ref er ence ma te rial (Geo chem i cal Soil and Till Ref er ence Ma te ri als cer ti fied by Breitländer Com pany). Changes in the ox ides con tent within soil pro file were eval u ated on the ba sis of for mu las given by Breemen and Buurman (1998), and Muhs et al (2001).…”

Geochemistry in the modern soil survey program

“…It has been useful in characterizing pedon and landscape processes such as direction or extent of weathering and determining the nature or origins of parent materials (Jersak et al 1997;Wilcke and Amelung 1996;Muhs et al 2001).…”