Abstract

The sequence described lies in the eastern Brooks Range in northeastern Alaska. Rocks of late Paleozoic age predominate but rocks as young as Jurassic are present. Rocks of Devonian and possibly older age occur in 2 E.-trending belts. In the southern belt the Skajit Limestone, 500-2600(?) ft thick, formerly believed to be of Silurian age, is now determined to be of Middle(?) and Late Devonian age. An unnamed unit of limestone and siltstone (Upper Devonian), 0-2500(?) ft thick, rests on the Skajit. The limestone-siltstone unit intertongues with and is overlain by an unnamed unit of slate and sandstone (Upper Devonian) 2000-4500 ft thick, which locally rests disconformably on the Skajit. The Kanayut Conglomerate (Upper Devonian), 0-5000 ft thick, conformably overlies the slate-sandstone unit and probably grades into it laterally. Rocks in the northern belt comprise the 4 members of the Neruokpuk Formation of Late(?) Devonian or older age; a quartzite-schist member more than 4000 ft thick, a limestone member 1000+ or - ft thick, a limestone-phyllite member 1000+ or - ft thick, and a phyllite-chert member as much as 3300 ft thick, which overlies the other members, locally with strong angular unconformity. The Kekiktuk Conglomerate, a new formation of Devonian or Mississippian age, 0-400 ft thick, unconformably overlies the Neruokpuk Formation. The formations of Mississippian age occur in both belts. The Kayak Shale (Lower Mississippian) and Kayak(?) Shale (Lower(?) and Upper Mississippian), 400-1200 ft thick, rest on the Kanayut and Kekiktuk conglomerates and, locally, on the Neruokpuk Formation. The Lisburne Group comprises 3 formations. The Wachsmuth Limestone (Lower Mississippian), 0-950 ft thick, disconformably overlies the Kayak Shale in the western part of the area. The Alapah Limestone (Upper Mississippian), 600-1950 ft thick, rests disconformably on the Wachsmuth Limestone. Where the Wachsmuth is absent, the Alapah rests conformably on the Kayak(?) Shale. The Wahoo Limestone (a new formation of Pennsylvanian(?) and Permian age), 0-1400 ft thick, overlies the Alapah with probable disconformity. The Siksikpuk Formation (Lower(?) Permian), is more than 600 ft thick and consists mostly of shale. It rests unconformably on the Wahoo Limestone at Galbraith Lake and on the Alapah Limestone W. of Galbraith Lake. E. of Galbraith Lake the Sadlerochit Formation (Permian and Triassic) overlies the Wahoo limestone. The Sadlerochit is more than 1000 ft thick, and consists of sandstone, siltstone,and shale. Unconformities suggest uplift during early Late Devonian time and folding during Late Devonian to Early Mississippian time. The regional unconformity between Mississippian and Permian rocks diminishes eastward and deposition may have been continuous through Pennsylvanian time in part of the eastern Brooks Range.

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