Correlating Petrographic, Core, and Outcrop Data to Define Depositional Facies Successions of Middle Ordovician Trenton-Black River Carbonates in Central and Western Pennsylvania

Kostelnik, Jaime, Christopher D. Laughrey, John A. Harper
Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey, Pittsburgh, PA

Complete sections of the Middle Ordovician Trenton and Black River Groups crop out at Union Furnace along route 453 between Tyrone and Water Street in central Pennsylvania. At this locality we measured and described in detail a 240 meter-thick section extending from the Loysburg Formation, just below the base of the Black River Group, to the top of the Coburn Formation, the uppermost formation of the Trenton Group. Our cm-scale outcrop descriptions defined facies successions indicative of deposition in both homoclinal and distally steepened carbonate ramp environments. The formations consist of cyclic sequences of interbedded peritidal to subtidal limestones and deeper water calcareous shales. In order to make a complete depositional and diagenetic assessment of these rocks, we supplemented our outcrop descriptions and interpretations with data acquired from petrographic analysis and from cores recovered adjacent to the Union Furnace outcrop. The core studies and petrographic analyses revealed a few additional features that are masked by deformation and weathering at the outcrop, but in general the facies recognized in outcrop are easily recognized in these cores. Utilizing this combination of core and outcrop descriptions, and microfacies determined from petrology, we identified various criteria for recognizing depositional facies of the Trenton and Black River groups in both whole-diameter and sidewall cores. These criteria can be applied to make accurate facies interpretations in the subsurface of western and north central Pennsylvania and perhaps the rest of the Appalachian basin where these carbonates are targets of active petroleum exploration.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004