Data Summary

Bedrock Geology of Pennsylvania

2001 - Pennsylvania Department of Conservation and Natural Resources



Online Viewer Application:

Two digital data sets, one for geologic units and faults and the other for dikes, have been prepared for Pennsylvania. The data sets were digitized primarily from the artwork used for the 1980 "Geologic Map of Pennsylvania" (Berg, T. M., Edmunds, W. E., Geyer, A. R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, scale 1:250,000) and from source materials used for that map. Many of the source materials had been published as page-sized maps and were digitized from this published paper copy (Berg, T. M., and Dodge, C. M., 1981, Atlas of preliminary geologic quadrangle maps of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 61, scale approx. 1:62,500). The other source materials consist of unpublished and published maps at various scales. It was beyond the scope of the project to incorporate revisions that had been made to the geologic units since the 1980 map was compiled; however, some updates to formational contacts, faults, and dikes, as well as to geologic nomenclature and ages, were incorporated where the revisions could be easily made.

The 1980 Pennsylvania state geologic map (Berg and others, 1980) shows the areal distribution of 194 bedrock geologic units. The units range in geologic age from Quaternary to Precambrian and encompass a wide variety of lithologies. The map was compiled and published in a transverse mercator projection at 1:250,000 scale. The two digital data sets include 195 geologic units, which, for the most part, closely correspond to those shown on the 1980 map. The data sets were prepared using ArcInfo software and are provided in a geographic coordinate system (units in decimal degrees). Although it is possible to portray digital data at any scale, the geologic formational contacts, faults, and dikes represented in these data sets are not intended to be used at any scale finer than 1:250,000.

The polygon attributes in the data set for geologic contacts and faults include unit number, map symbol, name, age, and three lithology categories that represent the general lithologic makeup of each geologic unit. Each arc (line) in the data set is attributed as one or more of the three general categories of contact, fault, or border. Contact lines are attributed according to the type of contact shown on the 1980 map (solid, dashed, queried, or arbitrary). Fault lines are similarly attributed (solid, dashed, or queried). Borders are attributed as either state boundaries, quadrangle boundaries, or the shoreline of Lake Erie. The data set for dikes consists of arcs attributed with unit number, map symbol, name, age, lithology, and type of dike (solid or dashed). It is anticipated that the digital data sets will be used for a variety of regional or statewide geographic-information-system applications, including water-resource and environmental studies, conservation and ecosystem management, mineral exploration, and regional land use planning and development.