GEOPHYSICAL INVESTIGATION OF A SPIT COMPLEX IN GLACIAL LAKE MAUMEE

As the Huron-Erie Lobe of the Laurentide Ice Sheet retreated, proglacial Lake Maumee was bounded to the west at the Fort Wayne Moraine, and grew eastward as the Erie Lobe receded. LiDAR data reveals subtle shoreline features which appear to be a spit complex upon which a cemetery now stands near Zulu, IN. The spit complex elevation is 241 m asl, and correlates to the Maumee high (I) stage of Lake Maumee. Further interpretation of the LiDAR data suggests a portion of Lincoln Highway to the southeast was an eroding headland related to the spit complex. Ground penetrating radar (GPR) and electrical resistivity surveys were used to investigate the spit complex. Electrical resistivity tests at two sites revealed a 3-layer system, with a resistive top layer making up the feature’s relief, a conductive middle layer, and a resistive bottom layer. At the Lincoln Highway ridge site, the resistivity test revealed a resistive top layer with a lens shape consistent with an overwash fan deposited by storm surge. GPR revealed a 2-layer system at each site, but did not penetrate past the second layer. The results of both GPR transects revealed a hummocky to chaotic top layer, with the Lincoln Highway ridge transect exhibiting possible wave-cut features to the northeast. A Vibracore sample of the top layer at the Lincoln Highway ridge site revealed sand and gravel, modified by pedogenesis to a depth of 0.85 m. A Geoprobe core confirmed that the top layer at the Zulu cemetery is also sand and gravel modified by pedogenesis to a depth of 1.5 m, and an underlying second layer of clay-rich diamicton. The finer-grained top layer at the cemetery site is explained as more distal sediment transported from the headland by longshore drift processes. The resistive bottom layer was not sampled. The results substantiate the working hypotheses that (1) Lincoln Highway ridge is an erosional headland in glacial Lake Maumee, and (2) the Zulu cemetery is a depositional spit extending from the Lincoln Highway headland. The strandline elevation and direction of sediment transport from the spit complex supports the notion of an active Fort Wayne outlet and easterly winds, respectively, during the Maumee high (1) stage of the lake.