Abstract The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest nonmarine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analysis of 25 limestone cores, along with detailed subsurface data from the Upper Freeport Formation in western Pennsylvania (Armstrong and Indiana counties), identified a large lacustrine/alluvial complex. The complex was drained by an anastomosed fluvial system containing a mosaic of subenvironments including extensive wetlands, densely vegetated swamp areas, and freshwater, carbonate-producing lakes. These lakes were small in size (several square kilometers), shallow, stratified, and connected by surface and groundwaters. Carbonate production was not triggered by evaporative concentration but by biogenic algal production in a sediment-starved system. Carbonates were continually being recycled, both physico-chemically and biologically. Siliciclastic wedges and predominance of reworked and traction-deposited carbonates favor a current-dominated, open lacustrine environment. Small-scale lake-level changes may have been controlled by climatic or depositional dynamics of the river system. The northern Appalachian Basin was an active foreland basin situated in the wet equatorial zone during Allegheny time. Through the use of modern analogs for carbonate lacustrine systems, as well as for anastomosed river systems, a model for the generation of nonmarine sequences within cyclothems was proposed. Tectonics (subsidence) may have been the driving force that controlled river drainage patterns. The evolution from an anastomosed to a single-channel system between tectonic pulses produced a mosaic of subenvironments that culminated in soil and swamp formation. This culmination explains the great lateral continuity of coal and underclay deposits. The low depositional gradient and unique combination of climate, tectonics, and eustatic level simply created a place where lake sediments and plant material could collect for a limited period of time.

Simulated weathering experiments on coals and shales demonstrate that the critical factors responsible for the generation of acid mine drainage (AMD) are the amounts of total sulfur, total carbonate, and the surface area of the pyrite. Total sulfur and carbonate carbon contents differ markedly among paleoenvironments whose distribution has been mapped for the Alleghenian strata of western Pennsylvania. Freshwater ( Estheria- bearing) shales have a mean total sulfur content of 0.15 percent and a mean carbonate carbon content of 0.54 percent. Brackish ( Lingula- bearing) shales have a mean total sulfur content of 2.40 percent and a mean carbonate carbon content of 0.14 percent. Marine ( Chonetes- bearing) shales have a mean total sulfur content of 0.95 percent and a mean carbonate carbon content of 0.63 percent In the simulated weathering experiments, the amount of acidity, sulfate, and total iron exhibit a well-defined positive linear relation with total sulfur in samples whose carbonate carbon content is ≦0.01 percent. Where carbonate carbon contents are >0.01 percent, the amount of acidity, sulfate, and total iron is considerably less, and the linear relation no longer exists. Anomalously high amounts of acidity, sulfate, and total iron were encountered in both samples devoid of and containing carbonate and were associated with samples containing a high relative percentage of framboidal pyrite and/or pyrite having a high specific surface area. Because determination of the percentage of framboidal pyrite is subjective, direct measurement of pyrite surface area is preferred.