QUATERNARY LOESS DEPOSITS OF THE UPPER MISSISSIPPI VALLEY DRIFTLESS AREA: A KEY QUATERNARY RECORD AND FUTURE PROSPECTS, A TRIBUTE TO J.C. KNOX

The loess of the Driftless Area of the Upper Mississippi Valley was studied by early scientists such as T.C. Chamberlain, and the landscape characteristics of the region played a role in acceptance of an eolian origin for the loess. Following acceptance, loess research in the Driftless Area focused on distribution and characteristics for soil survey and land evaluation, with few investigations into age, source, and depositional environment. The arrival of J.C. Knox at the University of Wisconsin in 1967 initiated a 40+ year program focusing on the Quaternary record of the Driftless Area, with loess as a major recurring theme of Knox and students.

Loess was central to the findings of Tod Frolking, who concluded the upland red clays long considered residuum included loess-derived clay minerals that illuviated deeply to the dolomite contact. Frolking also studied soil morphology along catenas in thick loess, concluding that hillslopes have been stable throughout the Holocene. Knox documented that hillslope sediment movement was a response to periglacial conditions that led to rapid rates of soil erosion, based on mass balance considerations in small watersheds. A common phrase heard by all of Knox’s students is that rates of hillslope erosion were double those of the period of highest accelerated agricultural erosion. This was often followed by a phrase Knox credited to R.V. Ruhe: “the Driftless Area was in the refrigerator.” Across the River in Minnesota, Joe Mason studied mass wasting deposits and plant macrofossils to demonstrate the periglacial environmental conditions. Peter Jacobs studied a section at Oil City with 6 loess or loess-derived units with paleosols that are younger than 790 ka, suggesting the Driftless Area contains the most complete record of loess in the upper Valley. David Leigh produced a loess stratigraphic framework that is the basis for mapping and classification of loess in the state, and in particular, he documented the age and depositional environment of the Roxana Silt. Former UW Geography major Randy Schaetzl is investigating source and dispersal patterns of loess in the Driftless Area and other Wisconsin regions. On-going research by Mason and Jacobs indicates that loess in the Driftless Area is genetically linked to loess west of the River and also to the east on the Green Bay Lobe land surface.