Reconciling Paleomagnetism and Pangea.

Abstract

Although an array of geological and geophysical data support the conventional (Wegenerian) paleogeographic model of Pangea in the Late Triassic-Early Jurassic, its configuration in pre-Late Triassic time has remained controversial for the last half-century. Late Carboniferous to Middle Triassic paleomagnetic data have been repeatedly shown to be incompatible with the conventional model, leading to alternative paleogeographic reconstructions, built to accomodate the paleomagnetic records. However, these models invariably require dubious tectonic transformations that lack supporting evidence in the form of structural relics. An altogether different explanation for the model-data incongruity invokes significant non-dipole geomagnetic fields, but this undermines a core assumption in paleomagnetism: the geocentric axial dipole hypothesis. As paleomagnetic analysis is the only quantitative method for determining paleolatitude in pre-Cretaceous time, this persisting discrepancy between the conventional model and the paleomagnetic data has come to be a first-order problem in tectonics and paleomagnetism. This dissertation explores the third and final hypothetical solution to this problem: that the discrepancy is due to systemic bias in the paleomagnetic data. This hypothesis is tested by collecting new, high-quality, Permian and Triassic paleomagnetic data from Laurussia and Gondwana, by conducting tests for quality and bias on the published paleomagnetic data, and by re-evaluating Pangea reconstructions in light of these findings. It is established that with use of accurate Euler parameters and high-fidelity paleomagnetic data, the conventional paleogeographic model can be reconciled with the Carboniferous-Middle Triassic paleomagnetic record. The findings of this dissertation thus imply that neither alternative reconstructions or significant non-dipole magnetic fields need to be invoked to resolve this long-standing problem. Furthermore, the documentation of systemic bias in the studied paleomagnetic data has broader implications for paleomagnetism and derivative work; namely that erroneously shallow inclinations (in sediments), among other forms of bias, are likely to be pervasive in the present paleomagnetic data.