TRANSITION FROM TRADITIONAL TO DIGITAL MAPPING TECHNIQUES: GEOLOGIC MAPPING IN A PORTION OF THE NEWARK BASIN, BUCKS COUNTY, PENNSYLVANIA

Detailed geologic mapping has not been conducted in Bucks County in over 60 years (Willard et al., 1959). Since then, substantial suburban and industrial development has taken place resulting in high demand for groundwater resources and water quality issues tied to land use. The Pennsylvania Geologic Survey completes1:24,000 scale geologic mapping utilizing a hybrid approach to digital geological mapping in portions of the Ambler, Hatboro, and Langhorne 7.5-minute quadrangles.This study utilizes the three-member subdivision of the Triassic Stockton Formation developed by Rima et al (1962) in Montgomery County to interpret the stratigraphic architecture of the Stockton Formation in the southern portion of the Newark Basin in Bucks County. These divisions are based on overall lithic character rather than individual depositional packages and therefore emphasize the spatial and stratigraphic variability of hydraulic properties within the Stockton Formation. In ascending order, these members are the lower member, consisting of coarse-grained arkosic sandstone and conglomerate, the middle member, consisting of fine to medium-grained sandstone, siltstone, and subordinate conglomerate, and the upper member, consisting of very fine-grained sandstone, siltstone, and claystone. Low bedding dips, subtle topography, and development limit bedrock outcrop availability and nearly all observations occur in streams.Prior to fieldwork, streams with the potential for exposing bedrock are identified by review of 1-meter resolution lidar imagery. Locations with high probability for bedrock exposure are marked as points and incorporated with previously collected structural data and draft contacts and faults in a web-based map.These data are available in the field via tablet computer and facilitate efficient data collection by limiting time spent searching for outcrop where efforts may be futile. Additionally, areas which may benefit from additional data for contact or structural control become immediately evident in the field. This methodology enabled the filling in of “data gaps” within the study area and contributed to at least 25% of the total number of stratigraphic and structural observations and assisted in providing sufficient data coverage for confident stratigraphic subdivision.