Growing acceptance of continental drift as expressed in the plate tectonics model leads to consideration of its use as a basis for investigating certain aspects of paleogeography and paleobiogeography. As a first step the geophysical, stratigraphic, and paleontologic data for the Cretaceous, with particular reference to mid-Cretaceous events were examined.

The final separation of South America and South Africa dates from about Aptian/Albian time, which implies that the Mid-Atlantic Ridge as a relief feature dates from about that time. Unless there was compensating downwarping a change in the volume of the oceanic basins would occur. The stratigraphic records of Africa, North America, and Western Europe show that the major transgressive and regressive movements are synchronous and that a major transgression began about that time, perhaps reflecting the ridge activity.

Major changes can be seen in the biogeography of mollusks, forams, and other groups between the Early and Late Cretaceous. Pre-Albian marine faunas in the Pacific regions are linked by a large number of taxa with faunas in the Atlantic-Mediterranean region. After the mid-Cretaceous there is a reduction in the cosmopolitan

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aspect and more intense provincialism. The biogeographic changes appear related to changing ocean basin configuration and initiation of the breakup of the circum-equatorial Tethys.

In the present preliminary phase of investigation firm conclusions cannot be drawn, but the convergence of such diverse approaches encourages the interpretation that ridge activity caused mid-Cretaceous biogeographic changes.

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