Evidence of a late Palaeozoic land connection between Appalachia and Iberia.
[sciencythoughts.blogspot.com]
Over the past 30 years, a broad consensus has emerged that repeated cycles of supercontinent amalgamation and dispersal have occurred since the end of the Archean, and these cycles have profoundly affected the Earth’s evolution. Less clear is whether the supercontinent changes its configuration during its existence due to internal stresses. Although the classical 'Wegenerian' configuration of Pangaea immediately prior to its Early Mesozoic breakup is well constrained, there remains uncertainty about its late Palaeozoic configuration. Two end member models have emerged; Pangaea-A, which is essentially the 'Wegenerian' fit, and Pangaea-B, based on palaeomagnetic data, in which Gondwana was located about 3000 km farther east relative to Laurasia, compared to the Pangaea-A configuration. A late Palaeozoic Pangaea-B configuration would require substantial lateral (dextral) shear along major faults, inferred by Edward Irving to have occurred between the middle Carboniferous and Late Triassic, in order to obtain the Wegenerian configuration before Pangaea breakup. More recent palaeomagnetic data have been used to support the transition from a Pangaea-B to a Pangaea-A configuration during the Permian, and in the most recent model, the transition occurred between 275 and 260 million years ago. However, geologic evidence that would distinguish between these hypotheses is lacking. Moreover, the validity of the palaeomagnetic data purported to support the Pangaea-B configuration has recently been challenged.