BEDROCK ELEVATION AND SEDIMENT THICKNESS MAPS FOR A PORTION OF THE GLACIATED APPALACHIAN PLATEAU, NORTHWESTERN PA

A regional bedrock elevation map has been completed for Erie County, PA (4,035 km²) using information culled from more than 5,000 water supply and oil and gas well records. Bedrock elevation was contoured by hand at a scale of 1:24,000 and digitized. Bedrock elevation ranges from 130-560 m across the study area and is characterized by a large upland region (>335 m) surrounded by a low relief, lower elevation basin edge adjacent to Lake Erie. Two prominent, deep bedrock valleys (300-600 m wide, a total of 77 km of length and at least 200 m deep) bisect the uplands in a northwest-southeast orientation and appear to join Elk Creek, a modern stream valley that drains northwest into Lake Erie. Approximately 50% of the region is covered by sediments that are less than 15m thick and another 41% of the region is blanketed by sediments that are less than 46m thick. These sediments consist of a variety of Wisconsinan end and ground moraines in addition to paleobeach deposits adjacent to Lake Erie. The thickest sediments are found in the bedrock valley fill materials that range from 137-185m deep. While this fill accounts for only 6% (+/-3%) of the surface, our initial volumetric estimates for the two prominent valleys are 2-4 km³ of sediment. These bedrock valley fill deposits are likely to contain sedimentological evidence of multiple ice advance and meltwater episodes during the Quaternary. The data in our maps provide valuable regional context for refinements to bedrock and/or surficial geologic mapping and more detailed investigations of bedrock and glacial landforms, glacial stratigraphy, paleodrainage, tectonic history, and more.