EARTH GEOGRAPHY FROM 400 TO 250 MA: A PALAEOMAGNETIC, FAUNAL AND FACIES REVIEW

Abstract

Palaeomagnetic and faunal data have been re-evaluated on a global basis for the period from 400 Ma (early mid-Devonian) to 250 Ma (latest Permian). The boundaries of the major terranes are considered and defined. Six new palaeogeographical maps at 30 Ma intervals, which ensure kinematic continuity, are presented for this period. The palaeomagnetic data are very useful for positioning terranes for the present-day North Atlantic area, of variable value for China and Tarim, and for much of the large superterrane of Gondwana (being notably poor during the Early Devonian and the Early Carboniferous), and are sparse or non-existent for much of the rest of Asia. The relative positions of Laurussia and Gondwana at the end of the Palaeozoic when they united to form Pangaea are discussed, and it is concluded that the most convincing reconstruction (Pangaea A) is obtained by assuming an octupole contribution of 10–15% in combination with the main dipole of the Earth's magnetic field. As well as faunal and palaeomagnetic data, the disposition of the major sediment types, including coal deposits, evaporites and glacial deposits, has also been considered, especially in the late Carboniferous and Permian.