ABSTRACT The Middle Paleozoic section of the Appalachian Plateau exhibits a mechanical stratigraphy defined by layers that emit seismic energy with unique signatures in response to a strain energy accumulated on time scales associated with local, regional, and plate-scale processes. The Earth is in a state of frictional equilibrium, which means that even small changes in effective stress cause brittle failure and the concomitant release of ambient seismic energy. Stress changes as low as 0.001 MPa, the level of stress changes during Earth tides or the transmission of a fluid pressure wave, can activate failure on critically oriented fractures. These phenomena lead to a release of ambient seismic energy, which can be mapped using seismic emission tomography (SET) methods to image fracture networks emitting coherent seismic waves. We used a buried array of 54 sondes to identify active fracture networks over a contiguous volume of 3.76 km 3 within Middle Paleozoic rocks hosting two Marcellus gas shale wells drilled under the Appalachian Plateau of Lycoming County, Pennsylvania, USA. We sampled ambient seismic emissions before and after two stimulations and found that the pattern was repeatable. The fracture patterns illuminated by ambient seismic emissions defined a mechanical stratigraphy populated by clouds of seismic activity separated by packages of beds emitting relatively less seismic energy. The unique attribute of the beds emitting less seismic energy is a lower least horizontal stress (S hmin ) relative to adjacent mechanical units in the section. These low stress beds include the bottom portion of both the Marcellus and Burket/Geneseo black shales. There are three thicker mechanical units carrying clouds of higher energy emissions. These three units include siltstones of the Brallier above the Burket/Geneseo package, silty shale beds of the Mahantango between the Marcellus and Burket/Geneseo packages, and Silurian-Devonian carbonates below the Marcellus package. In map view, emission patterns in the Brallier follow Alleghanian J2 joints. Patterns in the Mahantango are consistent with slip along columnar joint zones like those cutting upward in outcrops of shale on the Appalachian Plateau. In sum, SET reveals a mechanical stratigraphy based on the release of strain energy from three major units of the Middle Paleozoic section.

ABSTRACT A 3 ton (2.7 metric tonnes [t]), granitoid lonestone with Appalachian provenance was found in situ in offshore Devonian black shale in northeastern Kentucky, United States, and is denoted herein as the Robinson boulder, or lonestone, after its discoverer, Michael J. Robinson. This large boulder appears to have been displaced nearly 500 km from its source on the opposite margin of the Acadian/Neoacadian Appalachian foreland basin. While previous identifications of possible lonestones have been attributed to Pleistocene glacial events, scrutiny of this lonestone’s origin suggests that the boulder, which was embedded in the Upper Devonian Cleveland Shale Member of the Ohio Shale in northeastern Kentucky, is most likely a Devonian ice-rafted glacial dropstone. Notably, palynologic correlation with reported glacial diamictites elsewhere in the basin indicates such a source. Together, the dropstone and diamictites, separated by ~500 km, provide evidence for alpine glaciation in the ancient Acadian/Neoacadian orogen and for tidewater glaciers in the adjacent, eastern margin of the foreland basin. The latest Devonian marine transgression and Neoacadian foreland subsidence are interpreted to have been associated with tidewater glacial connections to the open sea. Importantly, the existence of this dropstone and its likely glacial precursor events require new considerations about contemporary black-shale sedimentation and the influence of tectonics on the delivery of glacial sediments to foreland basins.

ABSTRACT Zone-diagnostic Middle to Upper Devonian ammonoids and conodonts occur in a sequence of thin carbonate beds in siliciclastic sections along the Allegheny front and northern fold belt of central Pennsylvania. The lowest, in the upper Tully Formation, and the succeeding four in the Harrell Shale, are southward continuations of marker beds long known in the Tully Limestone and overlying basin, slope, and shelf facies of the Genesee Group of New York State. These pelagic beds are Appalachian Basin signals of transgressive condensed intervals within global high-sea-level episodes and are associated with a worldwide biotic overturn in the tropical marine realm. The Upper Givetian Tully Pharciceras amplexum bed has close lithic and faunal equivalents in the Taghanic biocrisis interval in Morocco and southern Europe. The Lower Frasnian styliolinid upper Genundewa Limestone, with the entry of Manticoceras , and, in the succeeding dark West River Shale, the Bluff Point Bed, with the entry of late Koenenites and early palmatolepid conodonts, are Appalachian highstand signals of the worldwide Timan bioevent transgression recognized in Western Australia, the Russian Platform, southern Europe, Morocco, western Canada, and now Pennsylvania. The widespread occurrences of discrete ammonoid beds, even in the more proximal or shoreward sedimentary settings of the Catskill Delta, reinforce the view that they accumulated under conditions of sequestered sediment supply when transgressions flooded the newly vegetated and deep-root-forested delta flats. As such, they overprinted or interrupted the westward progradation of siliciclastic sediments generated by mountain-building tectophases of the Acadian orogeny. The Lower Frasnian ammonoid Epitornoceras dennisoni n. sp., described herein, from the Crosby Beds in the Harrell Shale at Milesburg, Pennsylvania, is named in honor of John Dennison.

Abstract: The most extensive Permian tetrapod (amphibian and reptile) fossil records from the western USA (New Mexico to Texas) and South Africa have been used to define 11 land vertebrate faunachrons (LVFs). These are, in ascending order, the Coyotean, Seymouran, Mitchellcreekian, Redtankian, Littlecrotonian, Kapteinskraalian, Gamkan, Hoedemakeran, Steilkransian, Platbergian and Lootsbergian. These faunachrons provide a biochronological framework with which to assign ages to, and correlate, Permian tetrapod fossil assemblages. Intercalated marine strata, radioisotopic ages and magnetostratigraphy were used to correlate the Permian LVFs to the standard global chronostratigraphic scale with varying degrees of precision. Such correlations identified the following significant events in Permian tetrapod evolution: a Coyotean chronofaunal event (end Coyotean); Redtankian events (Mitchellcreekian–Littlecrotonian); Olson’s gap (late Littlecrotonian); a therapsid event (Kapteinskraalian); a dinocephalian extinction event (end Gamkan); and a latest Permian extinction event (Platbergian–Lootsbergian boundary). Problems of incompleteness, endemism and taxonomy, and the relative lack of non-biochronological age control continue to hinder the refinement and correlation of a Permian timescale based on tetrapod biochronology. Nevertheless, the global Permian timescale based on tetrapod biochronology is a robust tool for both global and regional age assignment and correlation. Advances in Permian tetrapod biochronology will come from new fossil discoveries, more detailed biostratigraphy and additional alpha taxonomic studies based on sound evolutionary taxonomic principles.