Glacial Features in the Western Gulf of Maine Inferred From High Resolution Bathymetric Data

Multibeam sonar surveys in the last decade have revealed submerged glacial features in the western Gulf of Maine (e.g., Valentine et al., 2003). Here we examine high-resolution multibeam bathymetric data acquired in 2001 and 2005 over Jeffreys Ledge to infer the origin of previously unrecognized small-scale marine glacial features. Ridges as high as 5 m appear throughout the length of Jeffreys Ledge in water depths of ~50 m. Bottom photographs of these features show boulders of up to 50 cm diameter in a flat sandy bottom devoid of finer material. These ridges are probably recessional moraines that have been reworked during lower relative sea level (~55 m below modern sea level). The moraine-like features imply stabilization of an ice margin along the length of Jeffreys Ledge. The central portion of Jeffreys Ledge also contains asymmetrical dune forms with a relief of 1-6 m and along-crest orientations trending NW-SE. These dunes may have formed during megaflood events with water flow toward the southwest. Streamlined bathymetric features with a relief of ~8 m and lengths up to 700 m occur east of Jeffreys Ledge. These features have similar dimensions but different orientations (N-S), as compared to southeast-oriented drumlins identified south of Cape Ann by Oldale et al. (1994). Dissimilar orientations of these drumlins are consistent with the lobate shape of the ice sheet and probable local ice flow directions. Numerous iceberg scours were observed in the basins east of Stellwagen Bank and Jeffreys Ledge with varying widths (50-300 m), scour depths (1-5 m) and lengths (3-10 km). Two dominant orientations of iceberg scours (E- W and N-S) were identified. Additional data such as seismic profiles, bottom photographs and bottom samples will further define the origin of these small-scale glacial features. Oldale, R.N., Knebel, H.J., Bothner, M.H., 1994, Geomorphology 9, 301-309. Valentine, P., Unger, T., Baker, J., 2003, U.S. Geological Survey Geologic Investigations Series Map I-2676C, scale 1:60,000.