PROXIMAL FACIES OF THE UPPER FREEPORT AND ASSOCIATED CYCLOTHEMS IN THE VICINITY OF THE ALLEGHENY FRONT, NORTHERN APPALACHIAN BASIN

Cyclothems in proximal facies between the Upper Kittanning (UK) and Brush Creek coal beds are defined by erosive bases of incised valley fill (IVF) deposits and by nearby correlated contacts between mature paleosols and the overlying regionally extensive coal bed.

Study of highwalls in the Upper Potomac coalfield (UPC) allows interpretation of lithic units from cores. This approach was extended to the Castleman coalfield (CC) and to boreholes and outcrops in SW and west-central PA. Our results show one to two Lower Freeport (LF) cycles. The UF limestone just below the Upper Freeport (UF) coal is reasssigned to a LF cycle. Mature paleosols, thick coal, and IVF sandstones define the UF cycle. C-S geochemistry and fossils from the UF roof shales show that the UF cyclothem had fresh-water "highstand" deposits that extended 350-400 km from the eastern KY shoreline to the Allegheny Front in MD and PA, indicating minimal marine influence during UF transgression and highstand in the Northern Appalachian Basin.

In the interval above the UF and below the BC cyclothems in SW PA, two cycles (lower = Mahoning) can be identified, but in the CC, these are based on only two thin units of redbeds and rooted flint clays (paleosols?) at the expected horizons. In the UPC, only one (Mahoning) cycle is certain because mature paleosols and IVF sandstones are indeterminate. We postulate significant tectonic uplift in the UPC above the UF cycle prior to the development of the Mahoning IVF deposits, as these roughly 15-m-thick paleovalley sandstones are thicker than IVF sandstones in the same interval near the eastern KY shoreline. An earlier more western phase of this uplift may have reduced marine influence and caused the widespread fresh-water roof shales and younger facies of the UF cycle.

In SW and west-central PA, UF cyclicity breaks down in 6 small patchy areas within the extensive region of normal UF cyclicity. Non-marine limestone and laminated (ponded-water) flint clay in these patches occur above and in place of the UF coal bed. These areas cannot be attributed to glacio-eustasy or climate change alone. Rather, non-marine limestone and laminated flint clay probably formed in ponds too deep for plants to form peat. Because these areas are roughly aligned and within 100 km of the Allegheny Front, they may have resulted from localized tectonic adjustments during deposition.