Publications

The Early Cambrian paleogeographic enigma arises when tectonic reconstructions are made using palaeoclimatic versus palaeomagnetic data that result in possibly contradictory tropical, mid-latitude, and south polar locations for major continents. For example, northwest Africa and Cadomia may have lain in a tropical zone (0° to +/−30° latitude) based on the presence of archaeocyath reefs, minor evaporites, and carbonate platforms at ca. 520 Ma +/− 5 Ma or, alternatively, northwest Africa and Cadomia may have lain in a south polar zone (90° to 60° south latitude) based on palaeomagnetic constraints. Greater Avalonia may have evolved independently from northwest Africa if a dropstone constraint implying polar latitudes at ca. 530 Ma and a palaeomagnetic constraint implying ca. 50° latitude at ca. 505 Ma are accommodated. We show here how counter-clockwise rotation of Gondwana during the Cambrian about an interior axis may solve the enigma. Gondwanan apparent polar wander becomes consistent with tropical conditions inferred for northwest Africa when adjusted to accommodate constraints placing the south pole near Peru for ca. 540–520 Ma. Concurrent counter-clockwise rotation of Baltica and Gondwana during the Middle Cambrian may have facilitated separation of Greater Avalonia from Baltica across dextral shear zones.