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.

A complex sequence of deformation produced the major central and southern trends of the Appalachian fold-and-thrust belt in the Roanoke recess, Virginia. The incipient recess first experienced the Appalachian-wide stress field, then shifted to far-field effects from incremental counterclockwise rotation of the shortening direction, which resulted in the Central Appalachian fold belt, and then shifted to incremental clockwise rotation, which produced the Southern Appalachian fold-and-thrust belt. We analyzed joints, veins, normal and reverse faults, stylolites, and paleoseismites from Mississippian strata at the structural front of the Southern Appalachian fold-and-thrust belt, and the adjacent Appalachian Plateau west of the recess. We distinguished seven deformational events using orientations, intersection relationships, fault-slip directions, and mineralization histories. Five of these sets represent late Paleozoic deformational events (A1–A5), with shortening directions that show an evolving Alleghanian fold-and-thrust belt in the recess. A1 (shortening trend 085°–265°) is consistent with the previously determined Appalachian-wide stress field and incipient layer-parallel shortening strain in middle Mississippian carbonates. A2 (trend 145°–325°) is a newly recognized event, herein called the Princeton event, which is consistent with dominant orientations of previously determined layer-parallel shortening strain, clastic dikes in Upper Mississippian strata, and stylolites. These far-field effects may mark high-angle basement faulting associated with development of the foredeep bulge during incipient thrusting along the Pulaski thrust system far in the hinterland. A3 (trend 120°–300°) corresponds to initiation of the major Central Appalachian deformation, which resulted in fold-and-thrust belt structures such as the North Mountain fault and Wills Mountain anticline, while A4 (trend 160°–340°) is associated with Southern Appalachian (e.g., St. Clair thrust and Glen Lyn footwall-syncline) structures. A5 (trend 010°–190°) represents late Alleghanian deformation of the Glen Lyn syncline, likely associated with blind thrusting coeval with emplacement of the nearby Pine Mountain thrust sheet. Two post-Alleghanian fracture sets, PA1 (joint trend 150°–330°) and PA2 (joint trend 060°–240°), are orthogonal; PA2 is younger. These joint sets are associated with strike-slip and normal faults that are compatible with some fault-plane solutions from the nearby Giles County seismic zone.

Continental crust is recycled into orogenic forelands by the distinct but inter- related processes of tectonic imbrication and sedimentary dispersal. Tectonic loading by the orogen drives flexural subsidence of a foreland basin, and the orogen provides a source of sedimentary detritus to fill the basin. Detrital zircons in Pennsylvanian-age sandstones in the Appalachian (Alleghanian) foreland basin reflect an Alleghanian orogenic source of recycled and primary detritus from Grenville-age basement rocks and Iapetan synrift rocks, which also yield pre-Grenville recycled craton-derived detrital zircons. Minor contributions are from Taconic- and Acadian-age plutons and accreted Gondwanan terranes. Ages of the detrital zircons show that most of the synorogenic clastic-wedge sediment was recycled from older continental crustal rocks. Cratonward thrusting of crystalline thrust sheets over the foreland recycles continental crustal rocks from the continental margin and thickens the continental crust. Along the Alleghanian foreland, the Blue Ridge thrust sheet of crystalline basement rocks and Piedmont thrust sheets of metasedimentary rocks represent imbrication and thickening of rocks of continental crustal composition. Both tectonic imbrication in foreland thrust sheets and sediment dispersal into the foreland basin recycle and thicken continental crust.

Abstract The Hudson Valley fold-thrust belt of eastern New York State involves a relatively thin sequence of shallow-marine Silurian and Lower Devonian strata. Because of the thinness of this sequence, structures of the belt are relatively small. Thus, first-order ramps and flats, and fault-related folds can be seen in their entirety at a single roadcut. A field trip in the southern half of the Hudson Valley fold-thrust belt, from the latitude of Catskill to the latitude of Rosendale, provides an opportunity to see many examples of these structures, and to discuss the three-dimensional architecture of fold-thrust belts in an orocline. In particular, we will see how along-strike changes in stratigraphy affect fold wavelength and the depth of detachment horizons. The trip also provides the opportunity to examine the relationship between mesoscopic structures (e.g., solution cleavage and veining) and first-order structures.

Studies of the physical stratigraphy and analyses of the Middle Pennsylvanian flora and fauna of some coal beds and marine units of the Breathitt Formation in Kentucky, the Pottsville and Allegheny Formations in Ohio, and the Kanawha Formation and Charleston Sandstone in West Virginia show a need for the revision of stratigraphic nomenclature of the Pottsville Formation and the lower part of the Allegheny Formation and equivalent strata. Attempts to project single stratigraphic elements from one region to another have resulted historically in multiple miscorrelations. A major marine unit (previously misidentifled as the Vanport limestone of the Breathitt and Allegheny Formations) is here named the Obryan Member of the Breathitt Formation in northeastern Kentucky and of the Allegheny Formation in southern Ohio. The Obryan is characterized by the fusulinid Beedeina ashlandensis Douglass and is correlated with the Columbiana Member of the Allegheny Formation in central Ohio, which also contains that fusulinid. This correlation and the correlation of the Boggs Limestone Member of the Pottsville Formation in Ohio with the Stoney Fork Member of the Breathitt Formation in Kentucky are supported by analyses of Middle Pennsylvanian conodonts. A preliminary zonation of conodonts for strata of the Pottsville and Allegheny Formations shows that the major marine units of these formations in Ohio are biostratigraphically distinct. The Obryan Member is locally absent, but its position is marked by overlying clay beds in many parts of Kentucky, Ohio, and West Virginia. The Vanport Limestone Member of the Allegheny Formation (as identified in Pennsylvania and central Ohio) is here correlated with the Zaleski Flint Member (Allegheny Formation) in southern Ohio. The Kilgore Flint Member (new name, Breathitt Formation), the informal Limekiln limestone and informal Flint Ridge flint (Breathitt Formation) in Kentucky, and the informal Kanawha black flint (Kanawha Formation) in West Virginia are correlated with the Putnam Hill Limestone Member (Allegheny Formation) in Ohio. These latter chert deposits are shoreward (southward and southeastward) facies of a marine unit deposited mostly in restricted estuaries and bays. The chert deposits appear to result from a widespread episode of silicification of fossiliferous marine siltstones and limestones that locally affected underlying peats and silts. The Kilgore and Obryan Members and their equivalents are used as the two principal stratigraphic marker beds for analyses of Middle Pennsylvanian sections extending across northeastern Kentucky from central Ohio to central West Virginia. Clay units and coal beds that overlie the Obryan Member contain flint clay beds (tonsteins) that are, in part, the product of volcanic ash falls. The range zones of selected palynomorphs from northeastern Kentucky and southeastern Ohio corroborate some of the correlations proposed herein.

Selected Middle Pennsylvanian coals and one Upper Pennsylvanian coal from three outcrop sections and one exploratory drillcore in the central and northern Appalachian basin were analyzed for their spore content. In the studied assemblages, the most frequently encountered taxa were species of Lycospora, Laevigatosporites, Punctatisporites, Densosporites (and related crassicinulate genera), Granulatisporites (and related sphaerotriangular genera), and Florinites . Mid-Middle Pennsylvanian assemblages are generally dominated by Lycospora , with L. pellucida , L. pusilla , L. granulata , L. orbicula , and L. micropapillata being the most common species. A few beds in this interval, however, show more even distributions of Lycospora (produced by arboreous lycopsids) and forms related to tree ferns, calamites, and cordaites. In general, a stratigraphic upward increase in tree fern taxa is observed, with upper Middle Pennsylvanian coals being codominated or dominated by tree fern spores. In addition, the range zones of the following taxa appear to be useful for palynologic delineation of Middle Pennsylvanian strata on both intra- and interbasinal scales: Microreticulatisporites sulcatus, Triquitrites sculptilis, Laevigatosporites globosus, Radiizonates difformis-rotatus, Torispora securis, Thymospora pseudothiessenii, Murospora kosankei, Mooreisporites inusitatus, Granasporites medius, Schulzospora, Densosporites, Schopfites, Lycospora, Cirratriradites , and Vestispora . The recognition of these taxa in Appalachian spore assemblages allows for comparison and correlation of Pennsylvanian strata in the Eastern and Western Interior basins of North America and the Upper Carboniferous of Western Europe.

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.

Abstract The geologic strip-map for Transect E-l cuts a swath from the Thousand Islands region on the New York-Ontario border to the Atlantic Ocean floor off Georges Bank (see Fig. 1). It includes portions of New York, Ontario and of all of the New England states. The western part, mainly in New York, belongs to the North American craton. The remainder of the onland portion, east of Logan's Line, belongs to the Appalachian Orogen. Southeastward from Logan's Line the transect crosses a series of distinctive terranes. Several of these terranes are believed to be exotic, and to have been accreted to the North American craton during the Paleozoic. Superposed on these are several grabens and half-grabens containing early Mesozoic sediments and mafic volcanics. There are also Mesozoic eruptive complexes of an alkalic nature cutting across the Appalachian Orogen from southern Quebec, across New England, and continuing as a chain of seamounts offshore. Cenozoic rocks are limited to a small, but significant occurrence near Brandon, Vermont (BL on Fig. 2) and a few occurrences in the Cape Cod region and on the adjacent islands in southeastern Massachusetts. Offshore the corridor passes over the Gulf of Maine and Long Island Platforms, thence across Georges Bank and into the North Atlantic Basin. The Gulf of Maine and Long Island Platforms (Fig. 2) are underlain by Paleozoic metamorphic and plutonic rocks and early Mesozoic grabens, as in the adjacent onland regions, but are partially covered offshore by a 1-3 km section of late Mesozoic and