Subsurface Rock Correlation Diagram



Figure 1. Stratigraphic correlations presented in this report are generally valid for the counties highlighted in orange (otherwise known as the study area).

The purpose of this open-file report is to provide an annotated correlation diagram that describes the relative age, stratigraphic position, naming conventions, geographic extent, and bibliographic data for subsurface rock units in western Pennsylvania (see extent of study area in Figure 1), with particular emphasis on those units that serve as oil and gas reservoirs in the Appalachian basin (i.e., west of the Allegheny structural front; Figure 1). The correlation chart illustrates subsurface stratigraphic units that are generally present from northwestern and northcentral Pennsylvania to the southwestern and southcentral portion of the state.

This report is provided as an updated, digital version of Pennsylvania Geological Survey Open-File Report OF-79-01 (Subsurface Rock Correlation Diagram, Allegheny Plateau, Pennsylvania, authored by John A. Harper in 1979) and incorporates the findings of several, more recent reports, particularly the Stratigraphic Correlation Chart of Pennsylvania (authored by Thomas M. Berg et al. in 1983); The Atlas of Major Appalachian Gas Plays (edited by John B. Roen and Brian J. Walker in 1996); and Characterization of Geologic Sequestration Opportunities in the MRCSP Region (authored by Lawrence H. Wickstrom et al. in 2005).

Not only does the current open-file report incorporate revisions in stratigraphic interpretations that have been made over the past twenty-eight years, but also provides graphical and tabular data in a user-friendly, interactive format. The stratigraphic correlation diagram initially opens as one, large graphical image, but is further divided into four parts (Permian to Mississippian-age units; Devonian-age units; Silurian to Ordovician-age units; and Cambrian to Precambrian-age units), which allows the user to zoom in to a subset of the diagram for accessing details of specific rock units. For each rock unit identified on the correlation diagram, there are links to tabular data that list its age, system, series, general geographic extent, and relevant Pennsylvania Geological Survey references. For those rock units that serve as oil or gas reservoirs in the study area, drillers’ “alias” names, additional maps, and/or more localized stratigraphic charts are included to further describe the naming conventions, location, and extent of the particular units. In addition, an interactive map of type log locations is provided to identify those wells throughout the study area that corroborate the stratigraphy in the digital subsurface rock correlation diagram.