Pangaea Early in the twentieth century the German scientist Alfred Wegener postulated that, commencing in the Mesozoic and continuing up to the present, a huge supercontinent, ‘Pangaea’ (meaning ‘all land’), had rifted and the fragmented components had moved apart as a result; this soon came to be generally known as continental drift. His interpretation was that South America and Africa began to separate in the Cretaceous, as did North America and Europe, but North America and Europe had retained contact in the north as late as the Quaternary. The Indian Ocean had begun to open up in the Jurassic but the principal movements took place in the Cretaceous and Tertiary.
Although Wegener's supercontinent was controversial for many years, the general outlines of his interpretation are now widely accepted, although parts of it have had to be modified as more information has become available. Thus no one accepts today that the final separation of North America and Europe took place in the Quaternary. With the use of the magnetic anomaly record of the ocean floor it is possible to trace the opening of the Atlantic and Indian Oceans in considerable detail. The earliest opening apparently took place in the Middle Jurassic, in the central sector of the Atlantic between the present United States and north-west Africa, followed slightly later by opening of the Mozambique Channel off East Africa. The principal separation of the continents took place, however, in the Cretaceous, with the South Atlantic commencing its opening, Western Europe separating from North America, and India separating from Australia, Africa, and Antarctica. In the early Tertiary the northernmost sector of the Atlantic, the Norwegian Sea, began to open, and North America became separated from Europe in the Eocene. The final separation of Australia from Antarctica also took place in the Early Tertiary.
Figure 1 shows a modern reconstruction of Pangaea on a Mercator-type projection, showing a number of geological tie-lines between the continents. The reconstruction is much more detailed than Wegener could attempt; it takes advantage of bathymetric and geological information unavailable to him, and uses least-squares computer fits of continental edges. The fit is awkward in two regions. There is some overlap of North and South America, and the Antarctic Peninsula does not align neatly, as the geology would suggest, with the Andean mountain chain of South America. It is believed that the reason for this lies in a mixture of continental stretching and strike-slip faulting between continental segments. Major modifications also have to be made of such Pangaea reconstructions undertaken in the years soon after the general acceptance of continental displacements and plate tectonics. It has become established within the past two decades that extensive parts of southern and eastern Asia have been accreted to the main Asian continent since the Late Palaeozoic, with a series of small continents progressively moving towards and suturing with the mainland (so-called displaced or exotic terranes). Thus, while western Pangaea was splitting up in the Mesozoic, north-eastern Pangaea experienced the reverse process.
Because of a positive hypsometric relationship between continental area and average height, Pangaea must have stood higher above the ocean level than the present dispersed smaller continents. It would also have induced a global monsoonal circulation rather than the zonal atmospheric circulation of today. Although the Mesozoic is generally considered to have experienced a more equable climate than that of the present day, the absence of polar ice caps in the Mesozoic must have resulted in considerable seasonal temperature extremes in the Pangaea climate, and much of the continental interior, far from the ocean, would have been arid in low latitudes.
Anthony Hallam
Bibliography
Embry, A. F., Beauchamp, B., and Glass, D. J. (eds) (1994) Pangea: global environments and resources. Canadian Society of Petroleum Geologists Memoir No. 17.
