1984 Articles

Paleomagnetism of Lower-Middle Devonian and Upper Proterozoic-Cambrian(?) Rocks from Mejeria (Mauritania, West Africa)

Kent, Dennis V.; Sougy, J. M. A.; Dia, O.

The paleomagnetism of two sedimentary rock units from the foreland of the Mauritanides of West Africa, in the Taganet region of Mauritania (Taoudeni basin) was studied to provide constraints on the paleocontinental positions of the southern continents in the Paleozoic. Thermal demagnetization of samples from the lower to middle Devonian Gneiguira supergroup isolated a predominantly single polarity characteristic magnetization (D = 135.7°, I = 27.3°, alpha 95 = 5.3° for N = 10 sites/44 samples) which gives a south paleopole position at Lat = 35.2°S, Long = 43.6°E (dp, dm = 3.0°, 5.6°). The only other direction sometimes present is one aligned near to the present dipole field axis, notably as a high temperature component of reversed polarity in 7 samples (D = 177.9°, I = −26.9°) obtained from 2 sites in weathered outcrop. The Upper Proterozoic to Cambrian (?) Mejeria red sandstone unit, equivalent to the Adrar CO10, although apparently unweathered has multicomponent magnetization. Most common is an intermediate temperature (300° to 550°C) direction (D = 137.2°, 1 = 14.4°, alpha95 = 13.2° for N = 4 sites/ 17 samples) similar to the characteristic direction of the Gneiguira. A high temperature component can be isolated in 11 samples but the directions are randomly distributed.
Comparison of the Gneiguira paleopole with other middle to late Paleozoic poles from Africa and Australia suggests that either it represents a Carboniferous remagnetization or that the south paleomagnetic pole for Gondwana already was off southern Africa by the Devonian. The paleogeographic and tectonic consequences of these possibilities differ considerably for the Atlantic bordering continents.