Rifting of Pangea and Formation of Present Ocean Basins

Abstract

At the end of the Paleozoic the supercontinent Pangea was surrounded by the “superocean” Panthalassa (all ocean). We have no way of knowing what islands, island arcs, spreading ridges, and other features most of the ocean contained, because all of it has now been subducted. We can, however, be somewhat more specific about continental fragments and spreading ridges in the small region of Panthalassa directly adjacent to the eastern margin of Pangea. This part of the ocean, known as “Tethys,” left a record of its history as continental fragments continued to rift from the Gondwana (southern) part of Pangea and move across Tethys to collide with the Laurasian (northeastern) margin of Pangea (chapter 8). During the Mesozoic and Cenozoic the positions and configurations of continents and ocean basins gradually attained their present form. Major continental reorganization resulted from movements of fragments across Tethys and the opening of the Atlantic, Indian, Arctic, and Antarctic Oceans and associated smaller seas. The size of Panthalassa, now known as the Pacific Ocean, gradually decreased as other oceans opened and small seas formed by a variety of processes in the western Pacific. Separation and collision of continental plates in what had been the center of Pangea formed the Gulf of Mexico–Caribbean and the Mediterranean. By creating new spreading centers, the breakup of Pangea generated a larger volume of young ocean lithosphere both in the new ocean basins and in the Pacific than the volume occupied by spreading centers in Panthalassa. By filling more of the ocean basins, these ridges forced seawater to rise eustatically onto continental platforms, creating shallow seas and filling cratonic basins where the crust was tectonically depressed. We begin this chapter by discussing the successive changes in Tethys and then the origin of the world’s major ocean basins. This is followed by an investigation of the smaller seas of the western Pacific region and the specific histories of the Gulf of Mexico–Caribbean and the Mediterranean. We continue with a discussion of the causes and locations of rifts that break up supercontinents and finish with a description of eustatic sealevel changes.