Using geospatial analyses to understand Laurentide ice sheet dynamics in New York State from landform morphometry and till fabric
Hess, Dale P.
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Streamlined subglacial bedforms are commonly used to determine the location of ice streams within former continental ice sheets. Moreover, the elongation of these features has been proposed to be a proxy measure of ice velocity and is therefore diagnostic of former ice sheet behavior. The mechanism by which these features form, specifically drumlins and megaflutes, continues to be a point of contention within glacial geomorphology research. As such, ice sheet reconstructions that utilize bedform morphometry as a measure of paleo-ice flow characteristics are tagged with a degree of uncertainty by some within the Quaternary research community. The trend and outline of 6566 subglacial bedforms in the New York Drumlin Field have been digitized from digital elevation data. The resulting display of bedform morphometry indicates the previous existence of at least two ice streams in the region (contrary to previous understanding of the Laurentide southern margin in New York State). Samples of drumlinized sediment were analyzed in thin section to evaluate specific mechanisms of subglacial bedform formation. The resulting observations imply a deforming bed model of bedform genesis thereby supporting the use of their elongation as an indication of former ice velocity. The manner in which subglacial sediment responds to applied stress remains a controversial subject. The orientation of clasts within till is commonly used to reconstruct ice flow direction, yet the mechanism by which particles rotate in a viscous medium remains unresolved. The three-dimensional alignment of large clasts is compared to the orientation of surrounding sand-sized grains. Based on the resulting observations, particles behave as passive markers during simple shear. The responsiveness of the particle varies with scale and supports the use of large clasts for fabric analysis, but sand-sized grains are respondent to local displacements and are therefore not representative of bulk deformation.