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 ° N, 14°E (k = 25, 0t95 = 8.8 °, 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 0nly 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.
Altermann, W. and Hiilbich, I.W., 1991. Structural history of the southwestern corner of the Kaapvaal Craton and the adjacent Namaqua realm: new observations and a reappraisal. Precambrian Res., 52:133-166.The rocks along the southwestern margin of the Kaapvaal Craton were deformed up to 7 times during the Early to Middle Proterozoic. The oldest deformation D, is recorded in the N-S-trending Uitkoms cataclasite of pre-Makganyene age ( > 2.24 Ga) on the craton, and interpreted as a bedding-parallel thrust. It is assumed to be a branch rising towards the surface from a blind sole thrust that initiated early N-S-trending F,-folds above it. D2 is represented by mainly N-S but also NE-SW and NW-SE-trending imbricates and recumbent fold zones ranging in size from small gravity slumps to large tectonic decollements in Asbesheuwel BIF and the Koegas Subgroup, and is younger than D1 or equals DI in age. These structures pre-date the Westerberg dyke-sheet intrusion. D 3 south-verging folds and thrusts are the oldest post-Matsap deformations, just less than 2.07-1.88 Ga. D4 are upright to east vergent and N-S-trending folds deforming all previous structures. D4 post-dates the Westerberg dyke-sheet and probably reactivates N-S folds above the earlier sole thrust during renewed E-W compression. Ds, producing the main NW-trending Namaqua structures, is only very feebly developed in the Kheis terrain and absent from the cratonic areas overlain by Olifantshoek and older strata, i.e. NE, E and SE of the Marydale High. Very gentle D6 E-W to ENE-WSW folds produce culminations and depressions in all NW-trending older structures. During D7 the NW-SE-trending Doornberg Lineament, an oblique left-lateral wrench, and smaller N-trending faults such as the Westerberg Fault developed. These and similar, but right-lateral faults are the last movements along the rim of the craton and occurred around 1.0 Ga.Multiple folding and thrusting with riebeckite mobilization happened prior to Namaqua events and resulted inter alia in discernable duplication and thickening of the Transvaal Supergroup along the southwestern margin of the Kaapvaal Craton and at least some 130 km into the craton interior. This complicates stratigraphic correlation as well as true thickness estimates of BIF units in Griqualand West, and affects the model for the environmental evolution of the Ghaap Group. A structural model of thin-skin decoupling at the base of the Transvaal Supergroup and starting in the MiddleEarly Proterozoic is proposed.
-Seven new and two re.surveyed stratigraphic sections through the important carbonate-BIF transition in Griqualand West are presented and compared with six published sections. Lateral correlation within this zone is attempted but the variability was found to be too great for meaningful subdivision. Substantial lithological irregularity is the only unifying character of this zone, for which the new name Finsch Member (Formation) is proposed. Vertical and lateral lithological variations as well as chemical changes across this zone are discussed with reference to environmental aspects. Local and regional considerations lead to the conclusion that fresh water-sea water mixing occurred in a shallowing basin.
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