PALEOECOLOGY OF PITTSBURGH FORMATION COAL BEDS (MONONGAHELA GROUP, LATE PENNSYLVANIAN) IN THE NORTHERN APPALACHIAN BASIN

A paleoecological assessment of the Pittsburgh, Redstone, and Sewickley coal beds, all of which occur in the Late Pennsylvanian Pittsburgh Formation of the northern Appalachian Basin, was conducted using palynologic petrographic, and geochemical data. Palynologically, all three coal beds are dominated by tree fern spore taxa, especially Punctatisporites minutus. Other common tree fern spores include Thymospora thiessenii, T. pseudothiessenii, Punctatosporites minutus, P. rotundus, and Spinosporites exiguus. Inter- and intra-bed abundance trends among some tree fern spore taxa are evident, especially for Thymospora. Calamite (Calamospora and Laevigatosporites spp.) spores are subdominant in all three coals, and small fern spores (e.g., Granulatisporites) generally rank third in abundance. Crassispora, the dispersed spore of Sigillaria, and Endosporites, which was produced by Chaloneria, are locally abundant. Pteridosperm (Schopfipollenites) and gymnosperm pollen grains (Florinites, Pityosporites, and others) are present in all three coals in minor amounts. Petrographically, all three coal beds are dominated by vitrinite macerals (usually > 80% on a mineral matter free [mmf] basis), with structured varieties (telinite and telocollinite) being more common than unstructured forms (desmocollinite, gelocollinite, and vitrodetrinite). Liptinite and inertinite macerals usually occur in low percentages (< 10%, mmf), but are locally abundant. Geochemically, all three coals have moderate ash yields (usually 10 to 15%, dry basis) and generally high (2 to 4%, dry basis), but variable, sulfur contents, the sulfur occurring mainly as pyrite. Ecologically, the Pittsburgh, Redstone, and Sewickley paleomires appear to have been widespread, rheotrophic mires dominated by ferns and calamites; other plant groups were minor components of the collective paleoflora. The high percentages of structured vitrinite suggest that the mire surfaces were kept moist a majority of the time by surficial waters. Interstitial peat waters were probably anoxic, and of variable acidity, given the range of pyrite abundance in all three coal beds. Fairly abundant fusinized plant remains on coal bedding planes indicate that wildfire, or intermittent oxidation, was common during peat accumulation.