SURFICIAL AND BEDROCK GEOLOGY OF THE NORTHERN MENOMINEE QUADRANGLE, JO DAVIESS COUNTY, IL

The northern portion of the Menominee 7.5’ Quadrangle was mapped as part of the EDMAP program to understand the landscape evolution history of the region throughout the Quaternary period and related to glaciation events. A clear understanding of the bedrock and surficial geology in this region is important to groundwater and agricultural land use management and sustainable development. The Menominee Quadrangle falls within an area in the northwestern region of Illinois and southwestern of Wisconsin known as the Driftless Area, i.e., a geologically unique region of the Midwestern U.S. due to the lack of direct glacial deposits (e.g., till or near glacial sand and gravel). Wind-blown loess deposits are significant in the region, however, there is no indication of till or proximal glacial deposits at the surface. Our mapping effort offers additional details and observations of the extent of Quaternary surficial deposits and bedrock exposures of the Menominee Quadrangle in Illinois northeast of the Mississippi River. We conducted multiple field excursions to observe and map the bedrock outcrops and verify surface deposit characteristics and thicknesses. We utilized the ClinoFieldMove application on iPhones and iPad minis to record observations and images in the field and exported the data as kmz files to import into ArcGIS. Remaining gaps in the map area that were not accessed during our field work were filled in with well data descriptions of soil, sediments, and bedrock. The final product of this project includes a georeferenced map generated and readily available geodatabase file for public access. Our results refined areas of bedrock and loess deposits across the mapping area. We also observed small areas of gravel deposits, including evidence of a thick glacial outwash deposit with cobble to pebble-sized dolomitic gravel on a ridge above the Mississippi River channel. We also verified that most of the surface deposits that we mapped were introduced to the Menominee Quadrangle primarily as wind-blown sand and silt (e.g., loess).