Abstract

Recent access to knowledge of ocean floors and continental margins has highlighted remarkable consistency in global structural history. The past 100 million years of that history, dominated by ocean spreading, is well documented and understood. But on all the aseismic continental margins there is evidence that oceanic opening was preceded by long-continued subsidence controlled by simple tension, a phase starting at least as early as Permian time.

What were the stresses within the continents during this period? Is there an implication of global expansion? How nearly contemporaneous were the changes from rift subsidence to progradation in widely separated areas? Do the Hercynian and Caledonian orogenies really compare with later continental collision phenomena? If they do, where are the oceanic (as distinct from geosynclinal) sediments of pre-Permian time? How can we explain the apparent continuity of Precambrian trends across the Iapetus suture?

Compilation of data on the history of the North Atlantic Ocean should go a long way in answering these and many other questions, fundamental to our comprehension of the structural history of the Earth.