Abstract A Marcellus-Burket/Geneseo field trip in the Appalachian Valley and Ridge features both brittle and ductile structures. The degree to which these structures have developed depends on both lithology, which is a function of the stratigraphic architecture of the Devonian Appalachian Basin and position relative to the foreland during the Alleghanian Orogeny. Joints are best developed in the black shales and the units immediately above with the J 2 joint set most prominent in the Brallier Formation just above the Burket/Geneseo Formation. Faults are seen in the form of cleavage duplexes and bedding-parallel slip accompanying flexural-slip folding. Cleavage duplexes are found in the Marcellus whereas bedding-parallel slip is more common in the overlying Mahantango Formation and further up the section in the Brallier Formation. Layer-parallel shortening decreases from greater than 50% to approximately 10% when crossing the Jacks Mountain–Berwick Anticline structural front from the hinterland portion to the foreland portion of the Valley and Ridge. Disjunctive cleavage, the primary mechanism for layer-parallel shortening, is best developed in carbonates whereas pencil cleavage is best developed in shales.

The Upper Devonian turbidite sequence in the central and southern Appalachian basin reaches 1400 m in thickness and consists of siltstone turbidites interbedded with mudstone, claystone, and shale. Facies and paleocurrent analyses, based on approximately 6100 m of detailed measured section at 35 localities and 700 measurements of directional structures, indicate major differences between the Upper Devonian sequence and submarine fan and ancient flysch deposits. Compared to flysch and submarine fan deposits, the Upper Devonian turbidites are finer grained and thinner bedded, reflecting the smaller size and lower maximum velocity of the turbidity currents. The stratigraphic transition from turbidites to overlying deltaic rocks shows a different succession from that expected for proximal deposits of submarine fans associated with fan channels and canyons. This transition in the Upper Devonian deposits is gradual and marked by upward-thickening and -coarsening sequences of evenly-bedded turbidites and lenticular beds of crossbedded sandstone. Higher energy mass flow deposits such as debris flows, massive and pebbly sandstone, and conglomerates are notably absent. Paleocurrent data are remarkably uniform, both areally and vertically through the stratigraphic section. They indicate a uniform dispersal pattern, transverse to the basin axis, for nearly 600 km along depositional strike. This suggests turbidity currents had multiple point sources along the basin margin and that the paleoslope had little topographic relief on it. Dip-oriented, short-lived turbidite lobes were built and abandoned as the source of turbidity currents shifted. Migrating delta distributaries, instead of fixed feeder channels, probably supplied sediment to the slope.