Paper No. 39-4
Presentation Time: 9:00 AM-6:30 PM

GPR IMAGING OF COASTAL SEDIMENTARY DEPOSITS ALONG THE LAKE SUPERIOR SHORELINE OF THE HURON MOUNTAINS, MICHIGAN, USA


JOL, Harry M., Department of Geography and Anthropology, University of Wisconsin-Eau Claire, Eau Claire, WI 54702, jolhm@uwec.edu, LOOPE, Walter L., United States Geological Survey, N8391 Sand Point Road, Munising, MI 49862, JOHNSTON, John W., Department of Geography, University of Toronto Mississauga, 3359 Mississauga Road N, South Building, Mississauga, ON L5L 1C6, Canada, BRECKENRIDGE, Andy J., Department of Natural Sciences, University of Wisconsin - Superior, Belknap and Catlin, P.O. Box 2000, Superior, WI 54880, LOOPE, Henry M., Department of Geography, University of Wisconsin-Madison, 550 N. Park St, 160 Science Hall, Madison, WI 53706, MORRISON, Sean M., Department of Geography and Anthropology, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54701, and JOL, Connor E., Roosevelt Elementary School, Eau Claire, WI 54703
Results from an investigation of the numerous progradational shoreline sequences along the pristine Lake Superior shoreline of the Huron Mountains are presented. The primary purpose of the field work was to test the feasibility of using ground penetrating radar (GPR) to image the historic and pre-historic shorelines of the littoral cell(s) and to establish if subsurface records could detect coastal stratigraphy.

The GPR acquisition systems used for the study were pulseEKKO 100 and 1000 with 50, 100 and 225 MHz antennae frequencies. Step sizes and antennae separation varied from 0.1 m to 2.0 m depending on the site conditions. Each trace was vertically stacked with a sampling rate adjusted to antennae frequency. The digital profiles were processed and plotted using pulseEKKO software. Basic processing included automatic gain control (AGC), signal saturation correction, trace stacking (horizontal averaging) and point stacking (running average). To calculate depth, near surface velocity measurements were calculated from CMP surveys. Topographic surveys, using a Topcon laser leveler, of the GPR traverses were performed to complete terrain corrections, and to compare the position of the subaerial stratrigraphy. The application of radar stratigraphic analysis (distinct signature patterns) on the collected data provided the framework to investigate both lateral and vertical geometry and stratification of the coastal deposits.

The GPR transects represent the first shallow geophysical profiles collected along Lake Superior’s shoreline of the Huron Mountains. The GPR transects record the shallow subsurface stratigraphy (>10-15 m depth) of episodically accreting beaches and dune ridges in this active littoral cell. The observed reflections from the collected profiles are interpreted as beachface and upper shoreface deposits of an actively prograding shoreline. The images also document the location of prehistoric and historic shoreline positions (lake levels). The results demonstrate that coastal sedimentary deposits can be mapped and show the utility of this geophysical tool as a regional, geomorphic mapping tool of coastal environments.