Abstract: Facies Architecture of Lowstand, Transgressive, and Highstand Systems Tracts in the Upper Devonian Lock Haven Formation, Council Run Field, North-Central Pennsylvania
LAUGHREY, C. D.
Pennsylvania Geological Survey, Pittsburgh, PA
D. A. BILLMAN
Geologic Consultant, Mars, PA
and M. R. CANICH, Eastern States Exploration Company, Alexandria, VA The Council Run field of north-central Pennsylvania is an important gas field in the central Appalachian basin. Cores and comprehensive well log control there permit the recognition of deltaic, shoreface, transitional, and offshore clastics within a sequence stratigraphic framework in the Upper Devonian Lock Haven Formation. A type-1 sequence boundary, at the base of the "Fifth Elk" reservoir sandstone, is overlain by a 15- to 40- m thick succession of strata interpreted as a lowstand systems tract. This succession originated as a lowstand-wedge deposited during a forced regression. Thick sandstones of this lowstand wedge pass upward into heterolithic sublittoral facies of the transgressive systems tract and, in turn, progradational parasequence sets of the highstand systems tract. An erosion surface, denoted by a transgressive lag, separates lowstand facies from overlying distal and intermediate offshore facies.
The resolution of sedimentary facies within a sequence stratigraphic framework at Council Run facilitates reservoir correlations, mapping, and interpretation of depositional environments. The "Fifth Elk" sandstone, for example, consists of two distinct upward coarsening facies associations capped by marine flooding surfaces. These parasequences within the lowstand systems tract record decreases in water depth. Both grain size and the ratios of sandstone to shale increase upwards in each parasequence. Sandstone bedsets and beds thicken upward. Bioturbation decreases upward to each parasequence boundary. Isopach and porosity maps reveal that the sandstones have a lobate to ribbon geometry. Palynomorphs, fossils, and trace fossils in the cores suggest deposition in a paralic setting. We interpret the "Fifth Elk" sandstone to have formed in beach and deltaic environments on a sandy, fluvial-dominated shoreline.
AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio