Expression of soil characteristics related to weathering and pedogenesis across a geomorphic surface of uniform age in Michigan

Randall J. Schaetzl,Leslie R. Mikesell and Michael N. Velbel

Our study explores the range of pedogenic development and near-surface weathering on a large (>250,000 ha) geomorphic surface in northern lower Michigan, via the examination of four typical soils. The surface is associated with proglacial outwash from the Port Huron advance of the Laurentide ice sheet, dated at about 13 ka. In a GIS we determined the four most extensive types of upland soils on this surface, and later sampled them. The range of expression on this outwash plain, when examined pedogenically or from a weathering perspective, is large, but is captured by these four soils. Numerical rankings along a number of pedogenic and weathering axes illustrated the considerable range of development, but they generally were consistent, i.e., rankings for pedogenesis roughly paralleled those for weathering. The most weakly developed soil ranked 3rd or 4th on almost all of the pedogenic and weathering-related parameters, whereas the other three soils exchanged ranks more freely, depending on the parameter being considered. The best developed soils on this surface are located in areas that receive more snowfall and, presumably, had less frequent fires since deglaciation, both of which drive pedogenesis and weathering in this region.

Soils on surfaces of uniform age are often used in relative dating applications, by assuming that soil development and weathering are related primarily to surface age. Our study shows that this assumption is violated on large geomorphic surfaces due to the variability of biotic and climatic factors across that surface. Thus, we suggest that the range and variability of soil expression must be considered in all soil chronofunction studies.