Abstract During the Pleistocene, the Laurentian Ice Sheet extended southward into western Pennsylvania. This field trip identifies a number of periglacial features from the Pittsburgh Low Plateau section to the Allegheny Mountain section of the Appalachian Plateaus Province that formed near the Pleistocene ice sheet front. Evidence of Pleistocene periglacial climate in this area includes glacial lake deposits in the Monongahela River valley near Morgantown, West Virginia, and Sphagnum peat bogs, rock cities, and patterned ground in plateau areas surrounding the Upper Youghiogheny River basin in Garrett County, Maryland, and the Laurel Highlands of Somerset County, Pennsylvania. In the high lying basins of the Allegheny Mountains, Pleistocene peat bogs still harbor species characteristic of more northerly latitudes due to local frost pocket conditions.

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.