A reliable 40Ar/39Ar plateau age of 180 ± 1.2 Ma (1σ) has been obtained for fresh basalt lava interbedded with aeolian Etjo Formation sandstones south-southwest of Grootfontein in northeast Namibia. This indicates that the Early Jurassic Karoo flood basalt sequence extended from Botswana into northeast Namibia at least as far as 18 east and that this may mark the eastern extent of the Early Cretaceous Etendeka Igneous Province. If so it would confirm the marked asymmetry of the Paraná-Etendeka Flood Basalt Province relative to the Atlantic Rift as noted by others. This age also supports the correlation of the Etjo Formation of the Waterberg Plateau, Namibia with the Clarens Formation of the Karoo Sequence in South Africa, and the use of the name ‘Twyfelfontein Formation’ for the aeolianites in the Etendeka region and its incorporation into the Cretaceous Etendeka Group.

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