Challenges in developing a Schmidt hammer exposure‐age dating calibration curve from glacial erratics in the North American Great Lakes

Abstract Schmidt hammer exposure‐age dating (SHD) ostensibly allows for rapid and cost‐effective deglaciation age estimates of presently undated glacial landforms, but this method requires a statistically strong relationship between Schmidt hammer data and landform age data (i.e. a calibration curve) to work. Schmidt hammer rebound values ( R ‐values) were measured on 34 glacial erratics in the U.S. State of Wisconsin that were previously dated using cosmogenic 10 Be exposure‐age geochronometry (~82–12 ka). Mean R ‐values ( R mean ) are reproducible between two Schmidt hammer operators; however, we observe no statistically meaningful relationship between R mean and erratic exposure age despite following similar methods that others have used to produce strong SHD calibration curves elsewhere. Furthermore, we observe no clear relationships between R mean values and geographic, topographic, lithological, environmental, and climatic factors at each erratic location. Our goal was to produce a SHD calibration curve for the North American Great Lakes region where geochronological data, which can be used to constrain the timing of Laurentide Ice Sheet retreat following the Last Glacial Maximum, are geographically sparse. Although we were unsuccessful in producing a SHD calibration curve, we do not believe our results are ‘negative’. We suggest that factors such as erratic transport distance, buildup of weathering residues on rock surfaces, erratic diminution during transport, the rate of fracture propagation through erratics, and others—all of which remain untested or unaccounted for in this study—may affect measured R ‐values.