Chemical and particle-size evidence for addition of fine dust to soils of the midwestern United States

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.