A new inclination shallowing correction of the Mauch Chunk Formation of Pennsylvania, based on high-field AIR results: Implications for the Carboniferous North American APW path and Pangea reconstructions

Abstract

A new magnetic anisotropy study was performed on samples of the Lower Carboniferous Mauch Chunk Formation of Pennsylvania. These red beds had been sampled for an inclination shallowing study by Tan and Kodama (2002), however, application of a high-field anisotropy of isothermal remanence magnetization (hf-AIR) technique specifically designed to measure the anisotropy of hematite provides considerably different results from those previously reported. The newly measured fabric has smaller anisotropy (~ 9–17% as opposed to ~ 25–40%) and shows a pronounced ENE–WSW magnetic lineation that is sub-parallel to the trend of the Appalachians and interpretable as a hematite intersection lineation that occurred during local NNW-directed shortening. The measured magnetic fabric yields a new inclination correction with a corrected paleopole that is in better agreement with recently corrected Carboniferous paleopoles than the previously corrected Mauch Chunk paleopole, defining a more consistent APW path. The corrected paleopoles allow calculation of new mean Early (~ 325 Ma) and Late (~ 312 Ma) Carboniferous inclination-corrected paleopoles for North America, which can be compared to coeval, but uncorrected, paleopoles from Gondwana. Results suggest a Pangea B assemblage unless inclination shallowing is considered for Gondwana. Estimating an inclination correction for Gondwana sedimentary rock-derived paleopoles permits a Pangea A-type assemblage at higher southern latitudes than previous reconstructions, which we term Pangea A3.