PRELIMINARY GEOPHYSICAL INVESTIGATIONS IN WESTERN LAKE ERIE

New seismic data obtained during fall 2006 have been used to refine the interpretations of the geology of the Lake Erie Western Basin. Previous interpretations show the extent and thickness of a possible delta/alluvial fan deposit offshore from the River Raisin. From that interpretation, Spongberg et al., identified sand bodies lakeward of the River Raisin mouth that were attributed to flow associated with the Nipissing Flood. However, the longest vibratory cores are 2.5 m and generally penetrate to the base of the recent lacustrine sediments, while some of the jetted holes are as deep as 10 meters. The sparse coverage did not allow definitive interpretations of sand bodies. Our current project adds high-resolution chirp seismic transects to the logs of previously collected vibratory cores and jetted holes. The seismic profiles provide needed continuity between widely spaced core holes, and show bedding geometries that can be correlated with lithologies from the cores and interpreted as depositional facies. To date, 170 km of seismic data have been collected to a depth of 45 m. Within the study area, there are windows of high-quality seismic data, but also sections of poor quality data because of abundant methane in the shallow sediments, which produces gas wipeout in the profiles. The overall goal of this project is to test the hypothesis that there are large deposits of sand in the Western Basin of Lake Erie and to infer the depositional processes that created the sand bodies. Preliminary interpretation of the seismic profiles reveals several unique surfaces and seismic facies that are tentatively identified as till, top of till, peri-glacial and glacio-lacustrine deposits, unconformities and recent lacustrine sediments. These facies interpretations will be evaluated by correlation with lithologies from the cores, especially the deeper jetted holes. Several of the surfaces bounding stratigraphic units, and the units themselves, can be traced regionally throughout the Western Basin. By defining primary stratigraphic units, and inferring depositional environments and processes, we will use these data to help constrain the late-glacial and post-glacial geologic history of this section of the Erie Basin. Further, existing radiocarbon ages will be integrated into the depositional history model.