Remagnetizations in late Permian and early triassic rocks from southern Africa and their implications for Pangea reconstructions

Abstract

A paleomagnetic study of late Paleozoic and early Mesozoic sedimentary rocks from southern Africa suggests wide-spread remagnetization of these rocks. Samples of the Mofdiahogolo Formation in Botswana and of the Lower Beaufort Group in South Africa were treated using thermal, alternating field and chemical demagnetization. The Mofdiahogolo redbeds show a univectoral decay of the remanence revealing a characteristic direction of D = 340[deg], I = -58[deg], K = 64, [alpha]95 = 12[deg]. The Lower Beaufort sandstones, using thermal and alternating field demagnetization, show a very similar direction of D = 337[deg], I = -63[deg], K = 91, [alpha]95 = 6[deg]. A fold test on the Beaufort rocks is negative indicating that this magnetization is secondary and acquired after the Permo-Triassic Cape Belt folding event. Previous studies have reported similar directions in the. Upper Beaufort redbeds as well as in the Kenyan Maji ya Chumvi Formation of Early Triassic age. The poles of these studies have been used in testing the validity of the various Pangea reconstructions for the Late Permian and the Early Triassic. Our results suggest that these poles may also be based on remagnetized data and that their use to document the position of Gondwana in Pangea reconstructions should be treated with caution.