USING GROUND PENETRATING RADAR IN THE OAK OPENINGS REGION OF OHIO

During the recession of the Huron-Erie lobe at the end of the last ice age ca. 13,000 years ago, a series of ice-contact proglacial lakes deposited lacustrine and littoral sediment across much of northwestern Ohio. The Oak Openings region is situated on the former beach of Lake Warren. A LIDAR-based digital elevation model (DEM) clearly shows a broad beachridge with parabolic and complex dune fields superimposed upon it.

While the DEM allows us to infer geologic events, it is necessary to explore the subsurface to gain a better understanding of the depth and extent of stratigraphic units, and ultimately, the geologic history of the region. Our primary research method is ground penetrating radar (GPR) to characterize the sub-surface stratigraphy. GPR is a non-invasive method in which electromagnetic waves are absorbed or reflected based on the sediment type they encounter. It works especially well in sandy environments, making the Oak Openings region ideal for GPR investigations. In our investigation, GPR is being used to map the thickness of the sand unit, distinguish between eolian and littoral structures, and locate the water table.

Several GPR transects were taken within the Whitehouse 7.5' Quadrangle study area, including the Girdham Rd. sand dunes in Oak Openings Metropark. Strike and dip transects reveal reflection surfaces to a depth of 16 m, below which the signal is attenuated. Interpreted transects reveal an eolian cap to a depth of approximately 6 m, underlain by littoral sediments to depth of 16 m. Elsewhere in study area total depth of sand was only 5 m. Fine-grained lacustrine sediments recovered in cores at lower elevations extend to an unknown depth below the sand.

This information, in addition to the GPR data and cores to be collected this summer, will allow us to map the subsurface stratigraphy of the region in detail. OSL samples are currently being processed from four sand dunes within the study area to determine if the dunes are deglacial or younger in age.