DEVONIAN TO MISSISSIPPIAN LITHOFACIES AND DEPOSITIONAL ENVIRONMENTS FROM DRILL CORE LYCO081_0341, LYCOMING COUNTY, PENNSYLVANIA

Bedrock geologic mapping as part of the STATEMAP program has focused on the Appalachian Plateau province of northern Pennsylvania where there has been natural gas development in the subsurface Marcellus Shale. The surface geology records a succession of Late Devonian – Pennsylvanian rocks that are largely of fluvial origin. As part of the geologic mapping efforts, a core was drilled in the Trout Run area of Lycoming County just north of Williamsport, PA. The core, LYC081_0341, was drilled to a depth of 1003.2 ft. and recovered the uppermost 382 ft. of the Catskill Formation (Devonian). The overlying Huntley Mountain Formation (Devonian – Mississippian) is 553 ft. thick and is overlain by the lowest 60 ft. of the Burgoon Sandstone (Mississippian).

The uppermost Catskill Formation consists of fining-upward packages of sandstone and siltstone/claystone. The sandstone is very fine to fine-grained, red to greenish-gray and is massive to cross-laminated. Fine-grained intervals of red silty claystone and clayey siltstone cap sandstone intervals. These fining-upwards cycles likely reflect deposition in moderate to high sinuosity river systems. The overlying Huntley Mountain Formation is a sandier succession with zones of green to red siltstone and minor claystone. The sandstone is greenish-gray and is very fine to fine-grained with zones of up to medium-size grains. The sandstone is commonly cross-laminated to cross-bedded. The siltstone is from greenish-gray to red and often contains intervals of calcareous nodules that are likely associated with paleosol development. Fining-upward packages are less well defined within the Huntley Mountain Formation, especially in the upper 300 ft. Here, sandstones are amalgamated into thicker zones from 44 to 95 ft. thick compared to 10 to 20 ft. thick that is observed in the Catskill Formation. The Huntley Mountain Formation was deposited in a fluvial system that was of a low to moderate sinuosity. The Burgoon Sandstone is 230 ft. thick in the study area, though only the lowest 60 ft. was recovered in the core. The Burgoon Sandstone is coarser and cleaner than the underlying Huntley Mountain Formation. It is crossbedded, white to gray in color and is fine to medium-grained with thinner intervals of coarse-grained sandstone. The Burgoon Sandstone was deposited in low sinuosity rivers.