Paleomagnetism of Permian sedimentary rocks from Tanzania and the Permian paleogeography of Pangea

Abstract

We report new paleomagnetic results from Karoo (Permian) rocks in Tanzania. K1 and K3 redbeds and K5 siltstones and limestones from the Songwe-Kiwira Basin, Ndeke redbeds from the Mikumi Basin, and group VIII redbeds from the Nyakatitu Basin were sampled and thermally demagnetized. Palynologic data and lithologic correlations suggest that the K1 redbeds are Lower Permian, and that the K3, Ndeke, and group VIII redbeds, as well as the K5 siltstones and limestones, are Upper Permian. Stable magnetic directions were obtained from the K3, Ndeke, and group VIII redbeds, yielding an Upper Permain pole at 26°N, 267°E. Characteristic remanence directions were also obtained from the K5 siltstones and limestones. However, because these directions define a pole (66°N, 269°E) that is very close to the Upper Cretaceous pole for Africa and significantly different from the Upper Permian redbed poles, these rocks may have been remagnetized. The K1 redbeds did not yield stable results. Using our new results together with published Permian poles for Africa and the other Gondwanan continents, we revise the mean Lower and Upper Permian poles for Africa, West Gondwana, and Gondwana, and investigate whether or not these revised poles can discriminate between the various Pangea reconstructions proposed for the Permian with any greater certainty than previous (unrevised) mean poles. When compared to the mean Lower and Upper Permian poles for Laurussia, we find that our revised West Gondwanan and Gondwanan poles do not necessarily provide stronger support for any particular Pangea reconstruction than the previous poles. Therefore, even though this study improves the paleomagnetic data base for Gondwana for the Permian, it is not clear that the combination of our results with other paleomagnetic data from the Gondwanan continents yields significant new insights about the Permian configuration of Pangea. As suggested previously, strong non-dipole fields during the Permian may provide an explanation for why it is not easy to discriminate with certainty between the various Permain Pangea reconstructions, even with new paleomagnetic results.