Tentative Paleocontinental Maps for the Early Phanerozoic and Proterozoic

Abstract

The maps are intended as an attempt to assemble the Early Phanerozoic paleomagnetic results in map-form so that in which they can be compared with the geological evidence. Relative longitude is estimated by minimizing relative motions among the continents. This approach also provides a useful means of discussing the "polarity problem" in constructing polar wander curves. Six stages are tentatively recognized: (1) at the end of the Precambrian the continental crust is assembled into a supercontinent with the Siberian Shield in the southern hemisphere adjacent to eastern Gondwana; (2) the supercontinent is fragmented in the Early Cambrian; (3) it is reassembled in the Late Silurian (Caledonian Orogeny); (4) undergoes internal adjustments in the Devonian by the sinistral rotation of Laurasia relative to Gondwana (Acadian Orogeny); (5) it breaks-up again in the Late Devonian; and (6) is reassembled in the Middle Carboniferous (Hercynian-Appalachian Orogeny). These succession of stages is regarded as the surface global expression of the Wilson Cycle. Experimental maps for the Late Proterozoic indicate that during the Grenvillian Orogeny there was dextral shear between Gondwana and Laurentia. It is stressed that the maps are not unique and have many inadequacies; e.g., they show no expression of the Taconic Orogeny.