SUBSURFACE GEOPHYSICAL PROFILING OF THE OAK OPENINGS SAND RIDGE

The Oak Openings Preserve extends from northwest Ohio into southeast Michigan. This unique area was shaped through glacial and glaciolacustrine processes to create a diversity of ecosystems including oak savannah, wet prairie, and sand barrens. The Oak Openings Sand Ridge is the primary landform within the preserve, and contrasts with the surrounding lake-bed plain to create these unique environments. Evidence suggests that the sand ridge was once a barrier bar system that developed during pro-glacial lakes Warren and Wayne. The area is home to more than a third of Ohio’s rare plant species and is on the Nature Conservancy’s list of Last Great Places. The environment that created these ecosystems is rare, and it is essential to understand the underlying geology and aquifer system in support of habitat restoration. Data was collected at Irwin Prairie, Shaffer Road, and Kitty Todd Nature Preserve which are all located just west of Toledo, Ohio. The data consisted of ground penetrating radar (GPR) and electrical resistivity transects, and a vibracore for ground truth. The stratigraphy at Irwin Prairie consists of a thick sand layer at the surface with a glacial till layer at a depth of 3.25m which acts as an aquitard. Irwin Prairie appears to be located in the back-barrier portion of the barrier bar complex. GPR data from Kitty Todd Nature Preserve indicates that it is situated on the ridge of the barrier bar complex, which is evidenced by large-scale sigmoidal bedding of a progradational spit. In contrast, the depositional environment of the Shaffer Road site is a shoreface that is prograding basinward, to the northeast. The modern investigative techniques allowed imaging of the subsurface to interpret the depositional environments and to characterize the surficial aquifer that created the physical setting of this unique and valuable ecosystem.