EVIDENCE FOR INITIAL OPENING OF THE PACIFIC OCEAN IN THE JURASSIC

An argument is presented for the east-west initial opening of the pacific Ocean during Early Jurassic times, on paleontological, biogeograhical, and geological grounds. A new reconstruction of the continents bordering the Pacific Ocean is proposed, based chiefly upon trans-Pacific, terrestrial biotic links that are not reflected in regions bordering the Atlantic. A new Arctic Ocean reconstruction is also proposed. Since the Atlantic and Indian Oceans were closed in the Early Jurassic as well, an expanding-earth model is adopted, instead of a Pangaen reconstruction on a present-sized earth. The model prposed here is also compatible with geological evidence for a narrow, epicontinental Tethys Sea. Sea-floor subduction along the perimeter of the Pacific appears to be actively taking place and in the past was much more extensive along the eastern border than on the western side. The tectonics of Antarctica, the Southwest Pacific, Indonesia, Japan, the Arctic region, western North America, Baja California, the Carribean, and the Gulf of Mexico are discussed in terms of the proposed model. The Pacific sea-floor spreading history is outlined and related to the initial opening of the North Atlantic 180 million years ago (Early Jurassic). The South Pacific and Indian Ocean are both considered to have opened some 155 million years ago (Late Jurassic). The original and present positions of the Jurassic equator are determined. © 1979.