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.

The rocks of the Pennsylvanian and Permian Systems of the central Appalachians are a series of shales and fine- to coarse-grained sandstones, locally conglomeratic, arranged in repetitious sequences with thinner coals, clays, lacustrine and marine limestones, chert, and ironstone. Isopachous and facies maps of arbitrarily selected thick units suggest two bodies of rocks, each with distinct orientations and distributions of swamp (organic) and lacustrine-marine (chemical) environments with respect to alluvial (deltaic) deposits. The earlier body, including the Pocahontas, New River, Kanawha, and Charleston, is a wedge of fine- to coarse-grained clastic rocks derived principally from older rocks of the Appalachians to the southeast. The sediments were deposited in a northeast-southwest–trending rapidly subsiding basin in western Virginia, southern West Virginia, and southeastern Kentucky. The coal-bearing facies thins rapidly to the northwest into massive marine (early) and deltaic (later) sandstones. The later body of rocks is divided into two groups distributed in a northerly deepening restricted basin of deposition. The lower group includes the Pottsville, Allegheny, and lower Conemaugh to the top of the Saltsburg Sandstone. Coarse- to fine-grained clastic sediments encroached on swamp, lacustrine, and marine environments in northeastern Kentucky, northern West Virginia, Maryland, Ohio, and Pennsylvania. The upper group includes the upper Conemaugh, Monongahela, and Dunkard, in ascending order. Fine (red)- to medium-grained clastic sediments of southwestern West Virginia and adjacent areas of Ohio and Kentucky encroached on swamp and lacustrine environments of northern West Virginia and contiguous areas of Maryland, Ohio, and Pennsylvania.

Detailed paleoecological analysis of the Upper Pennsylvanian Ames limestone and shale near Morgantown, West Virginia, suggests that the Ames transgression in that area was very rapid, presumably over a low-relief plain. Evidence of stillstand is in a lower Ames shale sequence immediately overlying the Harlem coal and, thus, is at odds with traditional interpretations which have placed stillstands in the limestone units of cyclothems. This interpretation is based upon a faunal analysis that resulted in the subdivision of the total Ames marine sequence into five communities: a basal stable mature community with maximum faunal diversity (stillstand); three distinct, and probably laterally adjacent, relict mature communities (regression); and an upper “mixed” community in the final regressive phase of the Ames marine event. The latter might be an assemblage, rather than a reflection of a once living community.