Paleomagnetism of the western Cape Fold belt, South Africa, and its bearing on the Paleozoic apparent polar wander path for Gondwana

In order to test two different proposals for the poorly defined African Paleozoic apparent polar wander path (APWP), a paleomagnetic study was carried out on Ordovician through Carboniferous clastic sediments from the Cape Fold belt, west of the 22nd meridian. One proposal involves a relatively simple APWP connecting the Ordovician Gondwana poles in North Africa with the Late Paleozoic poles to the east of South Africa in a more or less straight line crossing the present equator in the Devonian. The other proposal adds a loop to this path, connecting Ordovician poles in North Africa with poles to the southwest of South Africa and then returning to central Africa. This loop would occur mainly in Silurian time. New results reported herein yield paleopoles in northern and central Africa for Ordovician to lowermost Silurian and Lower to Middle Devonian formations. The best determined paleopole of our study is for the Early Ordovician Graafwater Formation and falls at 28[deg]N, 14[deg]E (k = 25, [alpha]95 = 8.8[deg], N = 28 samples). The other paleopoles are not based on sufficient numbers of samples, but can help to constrain the apparent polar wander path for Gondwana. Our results give only paleopoles well to the north of South Africa and we observe no directions within the proposed loop. Hence, if the loop is real, it must have been of relatively short duration (60-70 Ma) and be essentially of Silurian/Early Devonian age, implying very high drift velocities for Gondwana (with respect to the pole) during that interval.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26629/1/0000170.pd

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

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26063/1/0000137.pd