Characterizing glacial sediments and features in northeast Illinois using electrical resistivity and seismic-reflection profiling

Thick successions of glacial sediments are important components of shallow aquifer systems, wetland ecologies, and aggregate resources in northeast Illinois. Multiscale mapping studies have often utilized single surface geophysical methods to locally characterize and map geologic units. In this study, two-dimensional (2-D) electrical resistivity methods were combined with high-resolution shear-wave seismicrefl ection methods to better characterize glacial sediments and interpret geologic settings. Study sites were associated with sediments of a Wisconsinan phase of glaciation in northeast Illinois and included a regional bedrock valley, a buried tunnel valley, a pitted outwash fan, and an ice-marginal alluvial fan. Electrical resistivity methods were valuable tools with which to characterize textural relationships within geologic units, and they complement the seismic data with regard to stratigraphic boundaries. The seismic data indicated internal architectural features that were not resolvable with electrical resistivity methods. Thus, the combination of electrical methods and seismic methods improved both the detailed geologic characterization of natural resources as well as understanding of local glacial sedimentology.