Reconstruction of pre-Illinoian ice margins and glaciotectonic structures from airborne ElectroMagnetic (AEM) surveys at the western limit of Laurentide glaciation, Midcontinent U.S.A.

Early and early Middle Pleistocene glaciations in midcontinental USA are poorly understood relative to more recent Illinoian Wisconsinan glaciations, largely because pre-Illinoian glacial landforms deposits eroded buried. In this paper, we present a new interpretation of buried, features along the Laurentide margin northeastern Nebraska using Airborne ElectroMagnetics (AEM) supplemented with borehole logs 2 m LiDAR elevation data. We detect map large-scale (101–102 km) geological contrasts electrical resistivity. The limit is marked by continuous (>120 contrast between conductive (<15 Ω-m), clayey tills resistive (>40 Ω-m) sandy sediments. Several smaller (102 km2) till salients extend 10s km westward margin. recognize lithologically heterogeneous zone characterized variable resistivity complex geophysical structures extending as much 17 west limit. This interpreted glaciotectonic thrust complex, it analogous similar Denmark where structural analysis co-located seismic AEM surveys provides standard for comparison. Our study suggests that maximum advancement ice into involved extensive deformation sedimentary strata, local overriding these deformed strata tongues, emplacement 30 principal These insights provide first glimpse stratigraphic architecture sediments point future clarifications geology geomorphology