Abstract

Reconnaissance of the Brooks Range shows that this 125,000 sq km orogenic belt consists mainly of Devonian rocks. In the western Brooks Range two Devonian facies are juxtaposed. A group of clastic rocks, 2–3 km thick, consists of marine lutites that grade up into partly nonmarine Upper Devonian arenites and rudites, and continues upward in some places into Mississippian detrital and coaly beds. A group of carbonate rocks, more than 1 km thick, is characterized by Middle and Upper Devonian coralline and reef carbonates. Both groups are overlain with apparent continuity by Mississippian carbonates of the Lisburne Group, and therefore probably are synchronous for the most part. The differences in Devonian facies, as well as strong facies contrasts between Mississippian through Cretaceous rocks in sequence above the Devonian, suggest that two stratigraphic sequences were deposited in separate sites and were not juxtaposed before Cretaceous time.

This 100-km-wide belt of juxtaposed clastic and carbonate groups stretches eastward at least 350 km from Chuchi Sea. The carbonate group has been thrust upon the clastic group in the southwestern part of the range and upon rocks that lie above the clastic group in the northern part. The clastic group is present in outcrop and subsurface north of the carbonate sheet. The carbonate group may have been deposted 100 km south of its present position, possibly contiguous with similar carbonates in southeastern Seward Peninsula which themselves may have been displaced southward. A palinspastic map based on this interpretation provides a consistent picture of Devonian sedimentation between Wrangel Island (USSR) and the Canadian border.

The problems of the eastern limit of the overthrust sheet and of the structural relationship of Devonian rocks intermediate in facies between the two thrust sequences remain to be resolved.