Abstract

This study presents paleomagnetic results from the Oatka Creek Member of the Marcellus Formation. Paleomagnetic specimens were subsampled from a 50.8-mm-diameter subsurface drill core obtained from the Valley and Ridge physiographic province of Pennsylvania. Alternating field (AF) demagnetization techniques demonstrate that the Oatka Creek specimens retain multiple components of magnetization. The lowest-coercivity component, component A, was isolated by peak fields up to 20 mT and has characteristics of a drilling-induced remanence. Component B was isolated over a range of peak AF fields between 20 and 50 mT in the upper 100 m of the core, and points south with intermediate downward inclinations in geographic coordinates. Scanning electron microscopy, energy dispersive spectroscopy, and rock magnetic experiments yield evidence that suggests component B is a detrital remanent magnetization in magnetite. We corrected these directions for bedding tilt and inclination shallowing and calculated a paleopole at lat. 29.4°, long. 116.9°, A95 = 1.3°, with an age of 388–389 Ma constrained by biostratigraphy and radiometric dating. This paleomagnetic pole could help fill a data gap in the paleomagnetic record for North America that spans the Middle Devonian to Early Mississippian Periods. Component C was isolated throughout the core using AF fields between 50 and 100 mT and points south with shallow downward inclinations in geographic coordinates. Component C directions agree with a chemical remanence in pyrrhotite from a previous paleomagnetic study of the Marcellus Formation. Component C is likely also a chemical remanent magnetization in pyrrhotite acquired during maximum burial temperatures achieved in the Permian, which may have catalyzed pyrrhotite formation. Component D was isolated in specimens from the lower 20 m of the core, using peak AF fields between 20 and 100 mT, and it points north with shallow downward inclinations in geographic coordinates. The lower 20 m of the core shows evidence of significant hydrothermal alteration. The component D directions yield a paleopole in good agreement with the Jurassic reference pole, and a pulse of hydrothermal alteration in the lower portion of the Oatka Creek Member is consistent with other thermal events in the region ca. 180 Ma. Our results indicate that subsurface cores from the Appalachian foreland may provide an opportunity to greatly improve the Paleozoic paleomagnetic record for North America.

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