The Paleozoic section in the Shainin Lake area, central Brooks Range, Alaska

Abstract

The 7,500-8,000-foot-thick Paleozoic section exposed in the Shainin Lake area, central Brooks Range, northern Alaska, is divided into 5 formations, 4 of which have not been described before.The 3,300-foot-thick, probably nonmarine, Kanayut conglomerate (new name), of Late Devonian age, overlies an unnamed shale and sandstone, also of Late Devonian age.Massive lower and middle members of the Kanayut conglomerate are 1,400 and 1,030 feet thick, respectively.The upper, 860foot-thick, Stuver member (revised name), consists of alternating beds of shale, orthoquartzitic sandstone, and orthoquartzitic conglomerate.The overlying Kayak shale (new name), 960 feet thick, consists of black shale with a quartzose sandstone member at the base and argillaceous-limestone beds, which contain early Mississippian fossils, in the upper part.The Lisburne group (revised name), about 2,200 feet of fossiliferous bioclastic limestone and dolomite, is composed of 2 formations.The Wachsmuth limestone (new name), the lower 1,230 feet of the Lisburne, is predominantly cherty limestone and dolomite with some shale.Early Mississippian corals, echinoderms, bryozoans, and brachiopods occur sporadically throughout.The Alapah limestone (new name), the upper 970 feet of the Lisburne, is limestone with some chert and is characterized by late Mississippian lithostrotionoid corals and Gigantoproductus.Topmost beds of the Lisburne group are covered by high-level gravel deposits; the contact with overlying Permian or Triassic rocks is not exposed.Structurally the area is characterized by imbricate thrust faulting and high-angle reverse faulting.Mississippian rocks apparently represent platform-type deposition in an east-trending late Paleozoic seaway.