Late Cretaceous Chemical Remagnetization of the Paleozoic Carbonates from the Undeformed Foreland of the Western Canadian Cordillera

Abstract

Viscous remanent magnetization (VRM) recently acquired in the Earth's magnetic field provides a compass to recover in-situ orientation of unoriented core material. This method was used to date a late chemical remanent magnetization (CRM) in Paleozoic carbonate rocks (Devonian to Mississippian) from the foreland of the western Canadian Cordillera. The paleomagnetic data showed three distinct components: (1) a low-temperature component, which is commonly removed at temperatures below 180C and is assumed to be induced by drilling; (2) a medium-temperature component, which is commonly removed below 250–400C, with a steep normal polarity direction; and (3) a high-temperature component, which is isolated above 250–400C. In the foothills, high-temperature magnetizations always have steep reverse polarities, whereas in the Interior Plains, both normal and reverse polarities with more scattered inclinations are observed. The agreement between theoretical and laboratory blocking temperatures supports the interpretation that the medium-temperature component has recorded Earth's magnetic field over the normal polarity Brunhes epoch as a VRM. The same approach for the high-temperature component led to the interpretation that the high unblocking temperatures indicate a CRM event that affected the Paleozoic carbonates long after deposition. This component is equivalent to the A component observed by Enkin et al. (2000) in exposed strata. By correcting declination values using the medium-temperature component, the direction of the high-temperature component in the Interior Plains is D = 330.4, I = 74.3, k = 84, 95 = 3.4, N = 22 specimens, and in the foothills, it is D = 331.3, I = 82.4, k = 30, 95 = 8.1N = 12 specimens, corresponding to pole position consistent with the Late Cretaceous section of the North American apparent polar wander path.