Anisotropy-based inclination correction for the Moenave Formation and Wingate Sandstone: implications for Colorado Plateau rotation

*Correspondence: Kenneth P. Kodama, Department of Earth and Environmental Sciences, Lehigh University, 1 West Packer Ave., Bethlehem, PA, USA e-mail: [email protected] The ∼201 Ma paleopole for North America (NA) at the Triassic-Jurassic boundary (TJB) is observed in two widely different locations; one paleopole is determined from the Mesozoic rift basins in eastern NA and the other from the Colorado Plateau (CP) in the southwestern United States. A large discrepancy in paleopole positions from these two localities has been attributed to large amounts of clockwise vertical axis rotation of the CP (>10◦) combined with inclination shallowing of the paleomagnetism. The sedimentary inclinations of the eastern North American basins have been corrected for shallowing, but the CP inclinations have not. Simple vertical axis rotation of the CP is not enough to bring the two paleopoles into agreement. This study of the Moenave and Wingate Formations was conducted to correct CP inclinations using their high field isothermal remanent anisotropy. The Moenave Formation and laterally equivalent Wingate Sandstone, which span the TJB, were sampled in southern Utah and northern Arizona. Thermal demagnetization isolated a characteristic remanence carried by hematite from 20 sites. High field (5 T) isothermal remanent anisotropy indicated shallowing of the characteristic remanence with an average flattening factor of f = 0.69. An inclination-corrected paleopole for the Moenave and Wingate Formations is located at 62.5◦N 69.9◦E (α95 = 5.5◦) and is shifted northward by 2.9◦ with respect to the uncorrected paleopole. When the inclination corrected paleopole is rotated counterclockwise 9.7◦ about an Euler pole local to the CP, it is statistically indistinguishable from the inclination-corrected paleopole from the eastern North American rift basins. Rotation of the uncorrected paleopole does not bring it into statistical agreement with rift basin paleopole, therefore an inclination shallowing correction is necessary to support rotation of the CP and bring the Moenave and Wingate paleopoles into agreement with the eastern North American basin paleopole.