42 Geomorphology, Quaternary Geology and Marine/Coastal Geology (Posters)

Tuesday, 13 April 2010
8:30 AM - 12:00 PM
Taneycomo A

USING GEOPHYSICAL INVESTIGATIONS TO TEST THE CONCEPTUAL MODEL OF THE EVOLUTION OF THE GRAND MERE LAKES, SOUTHWESTERN MICHIGAN

Paper number: 42-4
Program: Technical Sessions
Time: 8:30 AM – 12:00 PM

Authors

Abstract

Grand Mere State Park is located on the southeastern coast of Lake Michigan in Berrien County. This area contains a suite of post-glacial lake shorelines. The three small Grand Mere lakes lie between the modern beach-dune complex to the west and former shorelines to the east. The east-west trending ridges between the lakes are hypothesized to be recurved spit platforms that developed from west to east, closing off successive lagoons. Various geophysical methods and a short vibracore were used to investigate the stratigraphy and its implications for depositional environments. 900 meters of ground-penetrating radar data, 300 meters of refraction seismic data, and over 600 meters of electrical resistivity data using both dipole-dipole and Wenner array formats were collected. The stratigraphy that emerged from the geophysical techniques includes: 1) up to 5m of surficial sand, deposited in a west-east direction, that thins to the north and south across the spit, 2) the presence of a paleochannel beneath the ridge at its eastern edge where it joins an older shoreline, and 3) beneath the sand, a ~5m thick, low resistive unit interpreted as lacustrine silt that overlies a higher resistive, possible sand body of unconstrained geometry. On the spit ridge, a hand-dug hole and 1.5m vibracore into the south side of the ridge, where the sand was thinner, recovered basal laminated sand and organic muck overlain by horizontally-bedded fine sand, cross-bedded coarse sand, massive sand, and modern soil. The observed and inferred subsurface stratigraphy is consistent with the conceptual model proposed by Anderson et al. (2010-this combined NC-SCGSA meeting) that the east-west ridges separating the modern Grand Mere lakes are spits and spit platforms created during the latter part of the Nipissing highstand.