Characterising the Triassic palaeomagnetic field: Implications for geomagnetic field evolution

• Main Author: Handford, Benjamin
• Other Authors: Biggin, Andy, Paterson, Greig, Hill, Mimi
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Geomagnetic Pole
• Online Access: http://livrepository.liverpool.ac.uk/3171162/; http://livrepository.liverpool.ac.uk/3171162/1/201089051_Nov2022.pdf

Records of the palaeomagnetic field are unique in their potential to provide insight into the evolution of the Earth’s interior. The geomagnetic field is a product of a dynamo process, and certain variations in the geomagnetic field at the Earth’s surface are reflective of variations in the Earth’s internal dynamics. Across time scales of tens of millions of years, such variations are proposed to reflect changes in core-mantle boundary conditions. Typically, variations in long-term geomagnetic field behaviour are expressed in terms of the frequency at which the geomagnetic field was experiencing polarity reversals, its average strength, and its stability. Of these measurable characteristics, it is changes in average polarity reversal frequency that are most well-defined. In particular, a relatively well-developed, continuous understanding of variations in average polarity reversal frequency has been established for the last 320 million years. Knowledge of average palaeointensity and palaeosecular variation (PSV) of the geomagnetic field, are less well established, with obvious shortcomings for the Triassic (ca. 251.9-201.3 Ma). This study aims to address these gaps by investigating the distribution of virtual geomagnetic pole dispersion, a common measure of PSV, during the Triassic, and conducting palaeointensity experiments on geological units that have previously been assigned Triassic dates. The study on PSV revealed a near-invariant latitudinal dependence of VGP dispersion for a time interval encompassing the Triassic, that was near-identical to that of the preceding time interval, as defined by average polarity reversal frequency. In contrast, the Permo-Carboniferous Reversed Superchron (PCRS), one of two such events during the last 320 million years in which polarity reversals were essentially absent, displayed an extreme example of VGP dispersion pattern that in part suggested that the PCRS was a time interval of enhanced axial dipole dominance. Successful palaeointensity estimates were deemed to be ...