Alexander K. Stewart, USA (ret)
Support
Evidence of a glacier’s basal movement can be challenging to discover due to subsequent weathering and covering by the retreating glacier. Thanks to mineral prospecting, however, in Talcville, NY, an approximately 0.3-hectare site of striated talc-tremolite schist became exposed for striae analyses. This “pit”, geologically, is part of the greater Frontenac Axis, which geomorphologically represents a hectometer-scale, northeast-southwest ridge-and-valley system (cf. Miller and Stewart, 2014). Using a compass, 2,901 azimuths of type-2 striations were measured across seven exposures (or pods) of polished whalebacks. In addition, 1,989 widths, 342 lengths, and 186 hardness measurements were collected using a caliper/measuring tape and hardness-testing kit. Using the EZ-ROSE program (Baas, 2000), all azimuths (n=2,901, mean of 011.6°, σ of 6.4°) were subjected to the Kuiper, Rayleigh, and Watson tests, all of which demonstrated a unimodal distribution with 99% confidence. Linear data were descriptively analyzed with mean striation length of 44mm (σ=7.0), width of 1.7 mm (σ=2.0), and Moh’s hardness of 5.1 (σ=2.1). Local joints and regional structure measure approximately 036-216° (Miller and Stewart, 2014) and are distinct from these striae suggesting the glacier flowed at an acute angle to the regional structure and topography. We estimate, by extrapolating our linear data, that at any one moment, 0.5-1.0㎥ of bedrock was removed from this site (approximately equal to the volume of a standard refrigerator’s interior). Inclusion of Moh’s hardness data suggests the striators must have been at least greater than the 5.1 hardness on average, but as high as 8.5, and, in conjunction with a 1-standard-deviation striae wedge up ice were likely sourced proximally from <35 km north or distally, from southern Quebec, CAN over 150 km away. Additionally, we infer that the flow of the glacier was not bedrock controlled, but likely deflected around the western Adirondack Mountains during an ice advance, as the glacier flow was more vigorous than topographic control, but not greater than the control of the western Adirondacks Mountain edge.