Abstract
M.Sc.
The Late Carboniferous to early Jurassic Karoo Supergroup of South Africa witnessed two of the “big five” Phanerozoic mass extinction events, and the formation and subsequent break-up of the supercontinent Pangea. The closure of the Permian Period witnessed the greatest biotic crisis in the history of life. What is known about the Permian-Triassic boundary (hereafter referred to as the PTB) comes almost exclusively from marine successions in Europe and Asia. Although a major extinction event has been recognized in terrestrial successions, surprisingly little is known about its effects and timing. The exact placement of the PTB in the Karoo basin is not well constrained due to shortcomings of stratigraphic methods employed to date. This has made it extremely difficult to correlate the mass extinction events in the marine and non-marine environments; however, paleomagnetic studies could provide answers to both problems of absolute placement and correlation of the PTB in non-marine and marine successions. The PTB appears to lie within an interval of reversed polarity in many marine successions. A detailed magnetostratigraphic survey across the presumed PTB in the Karoo succession at localities in the north and south of the main Karoo Bain reveal two magnetic chrons, reversed followed by normal (with the boundary close to the reversal), which extends to slightly younger results from a previous study that identified an N/R pattern, thereby identifying a R/N/R pattern. The normal chron might correlate with the long basal Triassic normal polarity interval and the reversed polarity zones above and below it known from marine successions in the Alps, Russia, Pakistan and China. The PTB is thought to be situated coincident with the LAD of Dicynodon and the event bed of Ward et al. (2000), apparently above but not necessarily diachronous with a lithology change from predominantly green- to predominantly red mudstone. This placement falls within a normal polarity interval, but could conceivably have taken place at a time of reverse polarity due to delayed acquisition of magnetic remanence. The idea of an extraterrestrial impact as the cause of the end-Permian mass extinctions is strongly enhanced by a synchronous relationship between them. The configuration of the supercontinent Pangea during this time of earth history has been the matter of debate for the last three decades, with numerous alternative reconstructions to the classic Pangea A1 having been proposed for the time preceding the Jurassic. Paleomagnetic data from the Karoo allow for the definition of a new paleopole for West Gondwanaland, which prove a valuable tool for evaluating these various reconstructions. It is neither consistent with a Pangea B-type not C reconstruction for Pangea during this time interval, because of geological ambiguities. The most likely solution to the problem is that of a persistent non-dipole field contribution to the geomagnetic field during this time. Approximately 50 million years later Pangea was unambiguously in a classic Pangea A1 configuration, and life on earth suffered yet another set back. The end-Triassic mass extinction, which marks the sequence boundary between the Triassic and the Jurassic, has not received as much attention as the other four big Phanerozoic biotic disasters. In the Karoo a pronounced turnover in faunal assemblages from typical Triassic fauna to Jurassic Fauna (dinosaurs) is seen in the Elliot Formation. Magnetostratigraphic study of localities in the north and south of the Karoo Basin provided a magnetic zonation pattern for the Elliot Formation, a tool that has led to the constraining of the sequence boundary to the transition from the lower Elliot Formation to the middle Elliot and added to the hypothesis that the faunal turnover is globally synchronous. The determination of a paleolatitude for the Elliot Formation in combination with characteristically arid lithologies (eolian sandstones) provided the base for the evaluation of the paleoclimate that characterized Pangea during the Late Triassic to Early Jurassic. Key words: Karoo Basin, Magnetostratigraphy, Mass Extinction, Paleoclimate, Paleogeography, Paleomagnetism, Pangea, Permian-Triassic, Triassic-Jurassic