SURFICIAL GEOLOGICAL MAP OF THE BLAKESLEE 7.5-MINUTE QUADRANGLE, PENNSYLVANIA

Pennsylvania was partially covered by the Laurentide Ice Sheet at least four times during the late Pleistocene, with glacial deposits mapped in portions of northwest and northeast Pennsylvania. The Blakeslee 7.5-minute quadrangle, located in northeastern Pennsylvania, straddles the terminal moraine complex of the late-Wisconsinan age advance. It contains a well-preserved geomorphic record of advance and retreat of the Laurentide Ice Sheet from the region as well as glacial deposits from an older, likely Illinoian age, and more extensive ice advance in the southern portion of the map. The terminal moraine of the late Wisconsinan ice sheet trends across the central portion of the map area and defines the maximum extent and advance of the Laurentide ice sheet during the Last Glacial Maximum. Other mapped surficial deposits include till, glacial outwash, alluvium, colluvium, wetlands, bedrock, and boulder fields. Surficial materials on steep to moderate slopes are subject to landslides and debris avalanches. Coarse-grained glaciofluvial and post-glacial fluvial deposits are potential high-quality drinking water sources and sources of economically important sand and gravel.

Previously published maps and recently acquired quality level 3 LiDAR derived elevation data (and map derivatives), aerial photographs, soil survey maps, and water well geologic data were used to update existing mapped surficial units. Select sites were field checked to verify and confirm the validity of the existing mapped surficial units. 10-Beryllium dating of three erratic quartz arenite boulders perched atop the terminal moraine complex will be used to provide a maximum limiting age for the late-Wisconsinan terminal moraine. Grain size analysis of sand/gravel deposits was used to characterize the textural properties of ice-contact stratified drift and glacial outwash deposits. All data is compiled into a 1:24,000 scale surficial geologic map.