SURFICIAL GEOLOGIC MAP OF THE CAMBRIDGE SPRINGS AND BLOOMING VALLEY 7.5 MINUTE QUADRANGLES, CRAWFORD COUNTY, PENNSYLVANIA

Northwestern Pennsylvania contains a series of Pleistocene glacial deposits that record as many as eight ice advances into the region. Aside from several regional studies conducted between 1950-1975, these deposits have been not been mapped in detail. A surficial geologic map for two contiguous 7.5’ quadrangles (Cambridge Springs and Blooming Valley) in eastern Crawford County was constructed using field exposures, soil maps, aerial photographs, and water well records. Field observations were collected from ninety three locations (road cuts, valley wall exposures, and gravel pits). Six distinct sediment units were identified and mapped; two are diamicts while the remaining four are coarse-textured deposits with varying amounts of sorting and/or stratification. The diamicts were deposited at the base of the ice sheet, and are interpreted to be the Late Wisconsinan Kent and Lavery lodgement tills. While there are textural differences between these two tills that are apparent in the field, we are exploring a mineralogic and/or geochemical means to distinguish between them. Three of the coarse-textured units were deposited by proglacial meltwater systems whereas the fourth unit is believed to have formed from meltwater in contact with ice along valley walls. Soils maps, coupled with aerial photographs, were used to delineate the contacts between each mapped unit. Sediment thickness patterns across the study area are based on geologic logs from water well records; more detailed logs allowed us to partially map the lateral and vertical extent of these units.