SURFICIAL GEOLOGIC MAPPING AND LANDSCAPE EVOLUTION RESEARCH IN THE DRIFTLESS AREA OF SOUTHWESTERN WISCONSIN

On-going surficial geology projects in the Driftless Area of southwestern Wisconsin are heavily invested in the concept of the valuable synergies between high-quality research and high-quality geologic mapping. Accurate and detailed mapping provides a basis to guide and inform original research; focused research leads to a better understanding of geologic process, events, chronology, stratigraphy and materials in a mapping area, and thus a better mapping product. To exemplify this, mapping along the lower Wisconsin River valley has provided the impetus to investigate the glacial deposits that define the boundaries of the unglaciated Driftless Area, and the Quaternary geologic history archived by those deposits.

Along the Mississippi River, south of the confluence with the Wisconsin River, coring has defined the easternmost extent of pre-Illinoian glacial deposits. Compact gray clay-rich till and associated outwash were recognized within 1 km of the modern Mississippi River underlying the ubiquitous Peoria loess. Coring through the pre-Illinoian Bridgeport moraine (Knox and Attig, 1988) identified a brown sandy till overlying a gray clay-rich till similar to that found farther south. This implies that multiple pre-Illinoian glacial advances, depositing markedly different till, extended eastward to a point roughly coincident with the modern Mississippi River.

In the Baraboo Hills area at the eastern margin of the Driftless Area, coring the late Wisconsin Johnstown moraine where it blocks the south end of the Devils Lake gorge has revealed the stratigraphy of the moraine and helped refine the history of the advance of ice to its maximum position. The moraine is composed of ~5 m of till overlying more than 75 m of sand and gravel (outwash). The stratigraphy suggests that ice was stable just short of its maximum extent and depositing outwash that the ice ultimately advanced over to deposit till on the outwash.

These data likely would not have been collected if not for the surficial geology mapping being conducted, and the insights gained from the data will improve the final mapping product. This highlights the concept that taking a research-driven approach to mapping facilitates developing priorities and long-term goals, and developing a greater understanding of key aspects of the geology of the area being mapped.