Multicomponent paleomagnetic data from the Nosoni Formation, eastern Klamath Mountains, California: Cratonic Permian primary directions with Jurassic overprints

Paleomagnetic data from the Guadelupian (Upper Permian) Nosoni Formation of the Redding Section (RS) consistently exhibit two directional components of magnetization in addition to a late Quaternary normal weathering overprint. Six sites in ash flow tuffs and tuffaceous sedimentary rocks, spanning 200 m of section, yield data that allow precise characterization of all components. Two additional sites in calcareous mudstones were too heavily overprinted to yield stable paleomagnetic directions. Thermal demagnetization of the tuffaceous samples in 16–18 steps between natural remanent magnetization and 660°C provides a detailed data base from which to calculate directional components. Analysis of demagnetization trends identifies a prefolding reversed direction carried by both magnetite and hematite and a postfolding normal direction carried by hematite only. Petrologic considerations suggest paragenesis of these oxides in the Permian (primary magnetite and hematite) and Early‐Middle Jurassic (metamorphic hematite). Least squares analysis of progressively demagnetized vector endpoint trends between 540° and 600°C yields a formation mean direction in magnetite having D =156.4°, I =−29.7°, k = 101, α 95 =7.6°. This result is in close agreement with the composite prefolding direction ( D = 160.3°, I =−31.5°), carried by both magnetite and hematite, determined by the intersection of remagnetization circles. The postfolding hematite‐carried overprint direction calculated by the latter technique has D =352.3°, I =35.0°. Paleopoles corresponding to these two directions are located at 57.6°N, 103.0°E (magnetite formation mean) and 67.0°N, 104.1°E (hematite overprint), coinciding within error to Upper Permian and Early Jurassic (respectively) reference poles from the North American craton. These data indicate no significant rotation or latitudinal translation of the sample sites with respect to cratonic North America since the Permian. This conclusion contrasts with seemingly reliable paleomagnetic results from elsewhere in the RS, which indicate major post‐Permian clockwise rotations. These rotations are evidently specific to individual structural domains and are probably manifestations of oroclinal bending about vertical axes.