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Most of Alaska is part of the Cordilleran fold belt. The cordilleras arose from several geosynclines, some of which took form in late Precambrian and early Paleozoic time, and others as late as Mesozoic time. Early deformational features in the middle Paleozoic have been largely obscured by Mesozoic and local Cenozoic orogenic events, especially along the Pacific margin. Plutonic rocks and thick wedges of coarse clastic sedimentary rocks, derived from uplifts within the geosynclines, identify the older orogenic events.
Easternmost Siberia, opposite Alaska, contains a fold belt that is the extension of the Cordilleran fold belt across the shallow Bering Sea from Alaska. In northern Alaska there also is a belt composed of probably early Paleozoic geosynclinal rocks and late Paleozoic and Mesozoic successor basin deposits that seems to correlate with the Innuitian fold belt of Canada. The continuity of these fold belts around the rim of the northern Pacific and Arctic basins must be taken into account in evaluating continental drift and the age of the ocean basins in the Arctic.
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