Abstract

North-trending folds and regional deflection of Cordilleran trends in the Bering Strait region strongly suggest east-west compression and crustal shortening between the North American and Eurasian continents during late Mesozoic or early Cenozoic time. Along the northwest coast of Alaska, the west- and southwest-trending grain of the Cordilleran belt appears to be deflected by a belt of folds and thrust faults that can be traced from Cape Lisburne southward across the Seward Peninsula and Yukon-Koyukuk province to the Kaltag fault. Fold axes are generally overturned to the east, and locally Paleozoic strata are thrust eastward onto Mesozoic strata. Major geologic trends on the north side of the Kaltag fault appear to be offset as much as 130 km to the east. On the Bering-Chukchi shelf, increasing evidence suggests that Cordilleran trends between Alaska and Siberia are buckled into a tight southward-looping orocline. The Paleozoic and early Mesozoic stratigraphic sequence on St. Lawrence Island is nearly identical with that found in the western Brooks Range, 400 km to the north, and distinctive belts of late Paleozoic and Mesozoic mafic volcanic and intrusive rocks and alkalic intrusive rocks appear to be traceable in an arc stretching southward from the Kobuk-Selawik area to St. Lawrence Island and then northward onto the Chukotsk Peninsula.

Oroclinal bending in the Bering Strait region and in the eastern Brooks Range appears to have foreshortened the northern part of the Alaska Cordillera by at least 800 km. As neither of these deflections is reflected in the arcuate trends of the Alaska and Aleutian Ranges, the northern part of Alaska may have been decoupled from the southern part along the Kaltag fault.

This compressional event in Late Cretaceous or early Tertiary time may be related to opening of the North Atlantic Ocean basin.

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