The Pittsburgh, Redstone, and Sewickley coal beds all occur in the Late Pennsylvanian Pittsburgh Formation of the Monongahela Group in the northern Appalachian Basin. The goal of this study is to compare and contrast the palynology, petrography, and geochemistry of the three coals, specifically with regard to mire formation, and the resulting impacts on coal composition and occurrence. Comparisons between thick (>1.0 m) and thin (<0.3 m) columns of each coal bed are made as well to document any changes that occur between more central and more peripheral areas of the three paleomires. The Pittsburgh coal bed, which is thick (>1m) and continuous over a very large area (over 17,800 km 2 ), consists of a rider coal zone (several benches of coal intercalated with clastic partings) and a main coal. The main coal contains two widespread bone coal, fusain, and carbonaceous shale partings that divide it into three parts: the breast coal at the top, the brick coal in the middle, and the bottom coal at the base. Thymospora thiessenii , a type of tree fern spore, is exceptionally abundant in the Pittsburgh coal and serves to distinguish it palynologically from the Redstone and Sewickley coal beds. Higher percentages of Crassispora kosankei (produced by Sigillaria , a lycopod tree), gymnosperm pollen, and inertinite are found in association with one of the extensive partings, but not in the other. There is little compositional difference between the thin and thick Pittsburgh columns that were analyzed. The Redstone coal bed is co-dominated by tree fern and calamite spores and contains no Thymospora thiessenii . Rather, Laevigatosporites minimus , Punctatisporites minutus , and Punctatisporites parvipunctatus are the most common tree fern representatives in the Redstone coal. Endosporites globiformis , which does not occur in the Pittsburgh coal, is commonly found near the base of the coal bed, and in and around inorganic partings. In this respect, Endosporites mimics the distribution of Crassispora kosankei in the Pittsburgh coal. Small fern spores are also more abundant in the Redstone coal bed than they are in the Pittsburgh coal. Overall, the Redstone coal bed contains more vitrinite, ash, and sulfur than the Pittsburgh coal. The distribution of the Redstone coal is much more podlike, indicating strong paleotopographic control on its development. Compositionally, there are major differences between the thin and thick Redstone columns, with higher amounts of Endosporites globiformis , gymnosperm pollen, inertinite, ash, and sulfur occurring in the thin column. The Sewickley coal bed is palynologically similar to the Redstone coal in that it is co-dominated by tree fern and calamite spores, with elevated percentages of small fern spores. Tree fern species distribution is different, however, with Thymospora thiessenii and T. pseudothiessenii being more prevalent in the Sewickley. The distribution of Crassispora kosankei in the Sewickley coal bed is similar to that in the Pittsburgh coal, i.e., more abundant at the base of the bed and around inorganic partings. By contrast, Endosporites is only rarely seen in the Sewickley coal. The Sewickley is more laterally continuous than the Redstone coal, but not nearly as thick and continuous as the Pittsburgh coal. Overall, the vitrinite content of the Sewickley coal is between that of the Pittsburgh (lowest) and Redstone (highest). Ash yields and sulfur contents are typically higher than in the Pittsburgh or Redstone. The thin and thick Sewickley columns are palynologically and petrographically very similar; ash and sulfur are both higher in the thin column.

Abstract The Redstone limestone of Platt and Platt (1877) is one of five nonmarine limestone beds in the Upper Pennsylvanian Monongahela Group. The Redstone limestone lies within the lower member (Berryhill and Swanson, 1962) of the Pittsburgh Formation between the thick, economically significant Pittsburgh coal bed (below) and the Redstone coal bed (above), and reaches a thickness of 12 m in some places. In addition to the autochthonous coal and limestone, beds of clay, shale, mudstone, siltstone, and sandstone also occur in the interval between the Pittsburgh and Redstone coal beds. The limestone occurs over at least 10,000 km 2 in the northern Appalachian Basin. The mineralogy of the Redstone limestone is predominantly calcite, ankerite, and quartz. In addition, dolomite, pyrite, feldspar, and clay minerals are present in smaller amounts. The carbonate minerals are most commonly micritic, but spar frequently fills voids in the limestone. Five carbonate facies were identified within the Redstone limestone beds: (1) desiccation breccia with paleosol characteristics, (2) nodular limestone composed of rounded limestone clasts, (3) fossiliferous limestone that is usually organic-rich, with plant debris, pyrite blebs, and nonmarine ostracods, gastropods, and bivalves, (4) massive micritic limestone, and (5) laminated limestone composed of dark and light gray micrite laminae 5 mm or less in thickness. Results of this study indicate that the Redstone limestone beds probably formed in a large, shallow, freshwater lake, or series of lakes, with regular influx of fresh water and fine-grained clastic material. Seasonal changes in rainfall caused wetting and drying of sediment along the shoreline and consequent paleosol development. These seasonal changes were also responsible for at least some of the lamination observed. There was enough wave and current activity to rip up, round, and redeposit intraclasts, and to cause breakage of many of the bivalves, gastropods, and crustaceans.

Abstract This guidebook chapter outlines a walking tour that provides an introduction to the geological, archaeological, and historical setting of Pittsburgh, with an emphasis on the use of local and imported geologic materials and resources in the eighteenth and nineteenth centuries. The focus is on downtown Pittsburgh, the low-lying triangle of land where the Monongahela and Allegheny Rivers join to form the Ohio River, and Coal Hill (Mount Washington), the escarpment along the Monongahela River to its south. Topics include the importance of—and concomitant effect of—historic coal use; use of local and imported geologic materials, including dimension stone used for buildings and gravestones, and chert used for gunflints and millstones; the frontier forts built at the site; and the ubiquitous landslides along Coal Hill.