Palaeomagnetic studies of the Etendeka volcanics and the resulting implications for the duration of volcanic activity and for magnetic field evolution in the early Cretaceous

There is a long-standing temporal correlation between large igneous provinces and major mass extinction events in the Geological Record. This is postulated to be due to the emission of large quantities of volcanic gases over a geologically short period of time causing major climatic perturbations within the Earth system. The Paran ́a – Etendeka large igneous province represents one of the few large igneous provinces where post volcanic environmental effects seem to have been minor. This thesis presents high resolution magnetostratigraphy from the Etendeka portion of the province accompanied by rock magnetic studies. The new high quality palaeomagnetic data identify 16 polarity chrons spanning the main volcanic activity. Following correlation to the geomagnetic polarity timescale, this suggests that volcanic activity occurred over a period of 4 – 5 Ma. Directional group analysis was conducted on continuous sections and revealed this volcanism to be non-pulsed. This extended and sporadic style of volcanism may explain the weak environmental effects of the Paran ́a – Etendeka. Given the high-quality of the palaeomagnetic directions, a study of palaeointensity was also conducted. This study yielded a series of high-quality estimates of Earth’s magnetic field intensity. The early Cretaceous marks an important change in the Earth’s magnetic field from a state of rapid polarity reversals, to one of long-term stability associated with the onset of the Cretaceous normal superchron at ≈ 121 Ma. Following palaeointensity estimation, numerous checks of data reliability were considered before results were accepted. The data revealed an overall average virtual dipole moment [VDM] for the study of 2.5 ± 1.0 x 10^22 Am^2. This value equates to approximately 30% of the present Earth’s field and, when considered alongside existing studies, suggests that Earth’s field strength was low in the time leading up to the Cretaceous normal superchron.