Jurassic Palaeogeography and Crustal Movements in North America

Abstract

Jurassic stratigraphy in North America has been recently promoted by IMLAY, FREBOLD and many other geologists. It seems important for Japanese stratigraphers to recognize the present status of the Mesozoic geology in North America especially its Pacific side, since Japan belongs also to the Circum-Pacific mobile belt which suffered somewhat similar orogenic disturbances in Mesozoic times.In this paper are summerized the stratigraphy, palaeogeography and tectonics concerning Jurassic rocks in Alaska, Canada and the United States (exclusive of the Gulf region) on the basis of such recent works, and compared with those in Japan. In North Alaska and Rocky regions the sedimentation was done under relatively calm and stable condition. But in many areas of South Alaska, the Canadian Coast Range and Sierra Nevada the Jurassic succession is fairly variable, of geosynclinal characters and the total thickness often excesses 5, 000 meters. The Jurassic period is generally recognized to be calm one without any strong orogenic disturbances in Japan and most countries, but in the Pacific coast of North America “Nevadan Orogeny” with initial magmatism, regional metamorphism, isoclinal folding, thrusting and batholitic intrusion took place during Jurassic and Early Cretaceous times.