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Volcanic and sedimentary strata of the Late Cretaceous MacColl Ridge Formation were sampled and demagnetized to reevaluate the paleomagnetically derived paleolatitude of the allochthonous Wrangellia terrane. Characteristic directions from 15 sites representing ϳ750 m of the MacColl Ridge Formation (80 Ma) reveal a reversed-polarity primary magnetization yielding a paleomagnetic pole at 126؇E, 68؇N, A 95 ‫؍‬ 9؇. Comparison of this pole with the Late Cretaceous reference pole for North America indicates 15؇ ؎ 8؇ of latitudinal displacement (northward) and 33؇ ؎ 25؇ of counterclockwise rotation. In contrast to previously reported low paleolatitudes (32؇ ؎ 9؇N) for the MacColl Ridge Formation, these new results place the Wrangellia terrane at a moderate paleolatitude (53؇ ؎ 8؇N) in the Late Cretaceous.

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The relationship between the remanent magnetization and the detailed strain geometry around a first‐order fold in the Appalachian Valley and Ridge Province was investigated to examine whether penetrative strains associated with folding can generate a apparent synfolding geometry from a prefolding magnetization. Paleomagnetic results from the Mississippian Mauch Chunk Formation on both limbs of the Frackville Anticline near Lavelle, Pennsylvania, yield two magnetic components, an intermediate unblocking temperature (300°C–600°C) Kiaman remagnetization and a two‐polarity high unblocking temperature (650°C–680°C) characteristic magnetization. When the magnetic directions are incrementally corrected for bedding tilt, the intermediate‐temperature component is most tightly clustered at 85% unfolding (D=176°, I=3°) and the high‐temperature component is most tightly clustered at 75% unfolding (D=184°, I=27°). Mesoscopic and microscopic structural fabric analyses suggest a strain history that includes a significant component of flexural slip/flow folding. In the coarser‐grained sandstone units, folding has largely been accommodated by slip on bedding, while in the finer‐grained beds, folding has been accommodated by grain‐scale deformation mechanisms such as pressure solution and low‐temperature plasticity. Finite strain measurements, determined from center‐to‐center distances between quartz grains, yield strain ellipsoids consistent with this folding model. Inclination of the characteristic component varies as a function of the magnitude of the finite strain. This variation suggests that the characteristic magnetization has been systematically reoriented with respect to bedding during folding. Remanence directions on the south dipping limb have been rotated to shallower inclinations, while those on the north dipping limb have been rotated to steeper directions causing the prefolding magnetization to appear synfolding. These rotations are in agreement with models of rigid particle rotation in deforming viscous media. Unlike the characteristic magnetization, the secondary component appears to be unaffected by the deformation, and its synfolding behavior is interpreted as the acquisition of a secondary magnetization during Alleghenian folding. These results show that it is important to consider penetrative strains when evaluating the significance of apparent synfolding magnetizations.