GROUND PENETRATING RADAR IMAGING OF A LAKE SUPERIOR HOLOCENE BARRIER: NEW INSIGHTS FROM LONESOME POINT, MICHIGAN

To better understand the Holocene chronology of the lake-level rise from the Houghton phase (low) to the peak Nipissing phase of ancestral Lake Superior, we have studied the spatial and temporal surface and subsurface patterns of an early-mid Holocene barrier located along the southeastern shore of Lake Superior at Lonesome Point, Michigan. Various methodologies, including ground penetrating radar (GPR), recording stratigraphic changes in lake-facing bluffs, as well as 14C and optical stimulation luminescence (OSL) dating, have been employed in reconstructing this massive barrier system.

The presentation continues this research and is dedicated to one of our collaborators, John B Anderton, a passionate instructor and field scientist, who was working on the project and passed away before its completion. Based on the earlier datasets and recent LiDAR imagery, the objective of the research was to continue to investigate the spatial subsurface patterns of Lonesome Point through the collection, processing, analysis and interpretation of a new 1660 m shore perpendicular GPR line to east of our previous cross barrier profile . The GPR system used for the study was a pulseEKKO 100 with 100 Mhz antennae and a 1000 V transmitter. Step size was 0.5 m, with an antennae separation of 1 m. Common midpoint surveys collected in the field were analyzed to determine a near surface velocity of 0.13 m/ns which was used to estimate depth of penetration (15 to > 30 m). Topography along the GPR line was collected using a laser level to geometrically adjust the resulting transect. The profile was processed using pusleEKKO software and applied an automatic gain control, dewow filter, trace-to-trace and down-trace averaging to the wiggle trace plot. The profile shows vertical aggradation and lateral progradation of a barrier beach environment deposited during the Nipissing transgression and regression. These deposits were preserved owing to positive sediment supply along this coastal reach from bluff erosion of the Grand Sable Banks and subsequent eastward longshore transport. The results will also aid in evaluating the relative roles of isostatic rebound and how climate change influences lake levels.