A new technique for measuring the magnetic fabric of hematite-bearing sedimentary rocks, hf-AIR: Inclination correction case studies of carboniferous red beds from the Maritime provinces of Canada

A paleomagnetic and rock magnetic study of the Lower Carboniferous red beds from the Shepody and Maringouin Formations of New Brunswick and Nova Scotia and from the Deer Lake Group of western Newfoundland was conducted for identifying and correcting inclination shallowing. Because of the shallow inclinations commonly observed in red beds and the strong dependence of North America's Paleozoic and Mesozoic apparent polar wander (APW) on red beds, inclination shallowing may substantially affect large portions of North America's APW path.;The potential of using high field IRM anisotropy measurements for determining the origin of natural remanent magnetization in red beds was investigated. The technique is made necessary by the inability of most paleomagnetic laboratories to demagnetize a high coercivity IRM without thermochemical alteration of the samplese. To overcome the difficulty of demagnetizing a high coercivity IRM between AIR orientations, the ability of 5T impulse DC magnetic fields to reset the magnetic moment of hematite was tested.;The individual particle anisotropy, or a factor, other fundamental parameter for an inclination correction was directly measured using a magnetic separation technique followed by setting of the samples in a DC magnetic field in order to align the grains. Assuming perfect alignment, the bulk remanence anisotropy of the samples, measured with AAR for magnetite or AIR for hematite, provides an average individual particle anisotropy.;Paleomagnetic directions of the hematite bearing Late Mississippian Shepody and Maringouin Formations and from the magnetite bearing Middle Mississippian Deer Lake Group red beds have been corrected for inclination shallowing. Results of the inclination corrections imply a ∼10° to ∼17° of inclination shallowing that follows the tan-tan relationship between remanent and field inclinations. The corrected paleopoles for the formations require a southward translation for this portion of North America's APW path that may significantly affect paleogeographic reconstructions. Finally, flattening factors f, the proportionality constants between the tangents of the observed remanent inclinations and the ambient field inclinations, were compiled from red bed inclination shallowing data, allowing to determine a range of inclination errors that can be expected for red bed formations that are suspected of being affected by inclination shallowing.