The sequence of rocks described lies primarily in the DeLong and Endicott Mountains in the western and central parts of the Brooks Range, northern Alaska. New names are given to dominantly siliceous and shaly sedimentary rocks of Mississippian through early Middle Jurassic age. The Kuna Formation (new name) consists dominantly of black bedded chert, shale, limestone, and dolomite within the Lisburne Group; some beds are phosphatic, and mafic extrusive igneous rocks occur in a few areas. Paleontologic data suggest an Early Mississippian to Early or Middle Pennsylvanian age for the Kuna Formation. Because the formation intertongues eastward with light-colored shallow-water carbonate rocks of the Wachsmuth and Alapah Limestones of the Lisburne Group, it is also assigned to t e Lisburne Group. Light-colored shallow-water carbonate rocks of other formations of the Lisburne Group were apparently also deposited on the south, but have been telescoped northward by thrust faulting over the darker Kuna Formation. The formation ranges up to 100 m in thickness. The Etivluk Group (new name) is composed of dominantly siliceous beds of the previously named Siksikpuk Formation and overlying Otuk Formation (new name). New paleontologic data suggest that the Siksikpuk is of Pennsylvanian, Permian, and Early Triassic age. The Otuk Formation consists of up to 100 m rhythmically interbedded chert, silicified limestone, and shale previously assigned in this area to the Shublik Formation. A thin but distinctive zone of early Middle Jurassic organic shale and dolomitic limestone ocally present within the top of the Otuk constitutes the Blankenship Member (new name), which is up to 7 m thick. Paleontologic data indicate that the Otuk Formation ranges in age from late Early Triassic to early Middle Jurassic.

These dominantly siliceous stratigraphic units appear to be limited to the allochthons of the western and central Brooks Range; they are not known to be present on the autochthonous complex of the northeastern Brooks Range and subsurface Arctic Slope.