GEOPHYSICAL INVESTIGATION OF MAGEE MARSH, LUCAS COUNTY, OHIO: EVIDENCE OF A PROGRADING BARRIER SPIT

The Magee Marsh Wildlife Area includes a barrier-island and marsh complex along the south shore of Lake Erie. Division of Wildlife. Few sections of the south shore have preserved long-term net deposition to create spits or strand plains. Historical aerial photos dating back to 1937 were evaluated for clues to the development of the Magee Marsh barrier island. Groins were constructed along the shoreline between 1940 and 1964. Sand deposition on the eastern sides of each groin indicates net westward littoral transport. One photo from 1957 shows a series of narrow spit shorelines extending west from a headland.

Investigation of the subsurface is needed to better understand the beach structure. Geophysical techniques used in this study include ground penetrating radar (GPR), Schlumberger vertical electrical soundings, and dipole-dipole resistivity surveys.

Three Schlumberger vertical electrical soundings were conducted. One dipole-dipole resistivity transect was run parallel to the Lake Erie shoreline. Two ground penetrating radar (GPR) transects were run parallel and perpendicular to the Lake Erie shoreline. GPR transect MG-1, which ran S-N, showed prograding sigmoidal beds, and the E-W MG-2 GPR transect confirmed progradation westward. Combined, these depict NW dipping, oblique-sigmoidal beds associated with the spit shorelines. Resistivity soundings support the stratigraphy inferred from the GPR and show ~2 m of sand overlying till and lacustrine silt, with bedrock at 15 m. When considering Magee Marsh’s closest island neighbor, West Sister Island, this surface is likely the eastward dipping Greenfield Dolomite of the Saline Group.

This study presents ample evidence of internal beach structures along the Magee Marsh beach barrier. The GPR profiles both westward and basinward support the interpretation of beach face progradation. We propose these sigmoidal beds represent NW progradation along a NW-SE trending barrier spit, with sediment transport toward Crane Creek to the NW. Further study of SE portion of the wildlife area may find littoral transport towards Turtle Creek to the SE.