Reconstruction of the Laurasian and Gondwanan segments of Permian Pangaea

Abstract

AbstractA reappraisal of the geological and geometrical constraints on the fits of the continents around the Atlantic, Indian and circum-Antarctic oceans is used as a base upon which to re-examine Early and Late Permian palaeomagnetic data. The palaeomagnetic poles from each of the three main Late Palaeozoic palaeo-continents: Eurasia, North America, and Gondwana define statistically well determined means for the Early and Late Permian. When these poles are reconstructed, the means, and their associated A95cones of confidence do not superimpose. The lack of superposition of Late Palaeozoic palaeomagnetic poles on Wegener-style Pangaea reconstructions based on Mesozoic and younger seafloor spreading geometries has been noted for some time. Most solutions to this problem have involved alternative 'tight fits' of the Pangaean continents for the Late Palaeozoic. Solutions invoking the non-dipole behaviour of the magnetic field have also been proposed. We examine the geometric consequences of the 'tight fit' Mesozoic-based Pangaean reconstructions that allow better fit of the palaeomagnetic data and conclude that the magnitudes of overlap (650-950 km) required by these modifications are not compatible with the geological and tectonic evidence from these regions. We prefer to use a 'looser' Pangaea fit that does not necessarily result in the superposition of palaeomagnetic poles. However, when the individual poles from Europe, North America, and Gondwana are combined into a global mean pole, it is observed that both the 'tight' and the 'loose' fit yield virtually indistinguishable mean pole positions. Considering the strong geological and geometrical arguments against the palaeomagnetically derived fits and the lack of a clear statistical difference between the two we use our revised Pangaean reconstruction to determine palaeo-latitudinal framework of the Eurasian, North American, and Gondwanan segments of Pangaea for the Early and Late Permian. The validity of these palaeo-latitudinal reconstructions is tested with climatically sensitive floristic and lithological data by Ziegler, and found to be satisfactory.