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Research on soil genesis often assumes a 'top-down' model, in which the soil profile develops downward from a stable land surface. This model is inapplicable to upland landscapes affected by frequent dust deposition, where soils grow upward as they develop. On the central Great Plains, late Quaternary loess sections proximal to immediate source areas contain the Brady Soil, a prominent marker separating late Pleistocene Peoria Loess from Holocene Bignell Loess. Farther from immediate dust source areas, the Brady Soil and Bignell Loess are not recognizable in the field. On loess tablelands in these distal regions, surface soils typically contain a prominent, clay-rich B horizon below a thick silty A horizon. Assuming top-down pedogenesis, this could be interpreted as a postglacial soil profile formed in Peoria Loess, with the B horizon produced by weathering and clay illuviation. We propose a strikingly different interpretation, in which the upper B horizon at distal sites is the Brady Soil A horizon that has been transformed by burial, organic matter loss, and modern subsoil structure formation processes. The overlying modern A horizon represents Bignell Loess. Properties of the Brady Soil at proximal sites (a distinctive burrowed zone, high clay content and Ti[O.sup.2]/Zr[O.sup.2], and low volcanic glass content) can be traced to the B horizon in distal soils. A decrease in smectite abundance above the Brady Soil at proximal sites is identifiable at the top of the clay-rich B horizon in distal soils. The spatial variation of clay content in loess and soil horizons is best explained by eolian sedimentation patterns. The higher clay content in the Brady Soil and distal B horizons defines a fine-grained zone that represents a late phase of Peoria Loess accumulation. Evidence of chemical weathering is minimal, and illuvial clay is rare to absent in the clay-rich B horizons. Illuvial clay does often occur deep in the solum and is related to the depth below the top of the Brady Soil. The depth of occurrence of illuvial clay is not related to modern climate parameters, although depth to secondary carbonate appears to be in equilibrium with modern climate. Upland soils in the central Great Plains are composite soils; their properties are the result of a pedosedimentary history linked to regional climate change that has influenced sedimentation and pedogenesis since the late Pleistocene. Keywords: Great Plains, soils, stratigraphy, loess, Holocene, paleosols.

Samples of 255 noncalcareous A, Ap, and AB horizons from selected major land resource areas (MLRA) in the north central USA were used to develop equations for predicting organic C content, as determined with a Leco C analyzer, from weight loss-on-ignition (LOI). Organic C concentrations of the samples ranged from 1.09 to 114.6 g [kg.sup.-1]. Within each MLRA, strong linear relationships were observed between LOI and organic C measured by the Leco instrument, with [r.sup.2] ranging from 0.94 to 0.98. Predictive equations developed by least-squares regression were significantly different for individual MLRA's. Loss-on-ignition is a rapid, inexpensive, and accurate for estimating organic C concentration in soils of the north central USA. We recommend that unique predictive equations be developed for individual soil-geographic regions.

Redoximorphic features are generally accepted to be reliable indicators of seasonal saturation although little data exist to verify or refine the relationship in southern Georgia. This 2-yr study used nested piezometers to investigate the relationship between seasonal saturation and redoximorphic features in seven pedons of the middle Coastal Plain near Valdosta, GA. Three clayey pedons including two Plinthic Kandi. udults and a Plinthaquic Paleudult were studied along a hillslope transect. Four sandy pedons including a Typic Quartzipsamment, a Grossarenic Kandiudult, a Grossarenic Kandiaquult, and an Ultic Alaquod were studied along an upland and river terrace transect. Results indicate that (i) pedons that experienced a seasonal high water table are endosaturated; (ii) a gray matrix is indicative of seasonal saturation, on average for >50% of the time, although some sandy horizons may be saturated much less; (iii) Fe depletions are associated with saturation an average of 18% of the study period, a value less than commonly reported; (iv) Fe-concentration features occur in horizons saturated on average for 24% of the time, although some shallow, especially sandy, horizons were never or only briefly saturated during the study period. Upland and backslope soils, especially Kandiudults with plinthite and reticulate mottling, do not show a consistent relationship between saturation and redoximorphic features; these features appear to be relict and more monitoring in a variety of landscape settings is needed to determine the origin and significance of these features.

Significant long-term atmospheric dust additions to soils are well documented in many parts of the world, but not in the midwestern United States. We investigated elemental mass fluxes associated with soil development in late Wisconsinan loess in Illinois and Minnesota, using Zr as a stable index element. Positive mass fluxes of Al, Fe, and Ti can most plausibly be explained by additions to these soils of fine far-traveled dust, with higher Al/Zr, Fe/Zr, and Ti/Zr ratios than the coarser locally derived loess. High-resolution particle-size analyses support this explanation. The proposed dust influx will complicate efforts to quantify weathering processes in these soils. Far-traveled dust influx could have occurred simultaneously with the final phase of local loess deposition, and/or later, in the Holocene. Depending on the timing of dust influx, many other soils of the region may have been affected by it.

Paleosols occur in the Driftless Area of southwestern Wisconsin because this area escaped direct Pleistocene glaciation, allowing long-term loess and colluvium accumulation in selected settings. The most complete known depositional sequence at Oil City, Wisconsin, contains eight lithologic units with five paleosols, all with normal remanent magnetism (i.e., <780 ka). Previous work characterized the stratigraphy, pedology, micromorphology, and clay mineralogy of the section. We investigate chemical weathering of the 8–63 µm silt fraction using X-ray diffraction (XRD) and elemental geochemistry by portable X-ray fluorescence (pXRF). Elemental ratios TiO2/CaO, Zr/Sr, and Rb/Sr generally align with the pedological evidence of weathering. Mineral ratios plagioclase/quartz and K-feldspar/quartz display greater scatter and less certainty in interpretation. The paleosols with Bt horizons have ratios indicating greater weathering than the modern soil. The most weathered paleosol is formed in the unnamed fourth loess unit stratigraphically below the Loveland Member. The stratigraphic position and higher degree of weathering support correlation of the fourth loess with the Yarmouth Geosol and Crowley’s Ridge Silt of the Middle Mississippi valley. Geochemical indices by pXRF are more consistent with established lithologic breaks than mineralogy by XRD. Our results support the use of pXRF for stratigraphic and weathering studies of Quaternary sediments. [ABSTRACT FROM AUTHOR]