Cambrian through Middle Devonian fossiliferous rocks define 3 depositional elements in Alaska: a carbonate platform near the craton in the Porcupine Plateau and north of the northeast Brooks Range; a shale-chert-volcanic basin south and west of this platform in the Ogilvie Mountains, Yukon-Tanana Upland, northeast Brooks Range, and probably along the Arctic Coast; and two linear segments of an outer carbonate platform--one trending westward from the southern Brooks Range to Seward Peninsula and St. Lawrence Island, the other southwestward from the Yukon-Tanana Upland to the lower Kuskokwim River. Early Paleozoic orogeny in the northeast Brooks Range is indicated by Silurian (430 m.y.) granite and a post-Cambrian unconformity within pre-Mississippian rocks.

A thick wedge of Upper Devonian terrigenous clastic strata in the Brooks Range north and east of Upper Devonian carbonates indicates a Late Devonian orogeny farther north. Regional angular unconformity beneath Mississippian rocks, and a Late Devonian-Early Mississippian granite mark the position of the orogenic belt along the Arctic Coast, northeast Brooks Range, and northern Porcupine Plateau. Upper Devonian turbidite conglomerates also indicate uplift south of the Porcupine Plateau and in the Yukon-Tanana Upland.

Mississippian and Pennsylvanian carbonates lap northward and eastward from the Brooks Range across a platform of folded Precambrian (?) to Devonian rocks on the Arctic Coast and northern Porcupine Plateau. Permian uplift along the Arctic Coast is indicated by the fact that coarse Permian clastic sediments were shed southward into the Brooks Range. A regional unconformity beneath Permian quartzose clastics indicates other uplifts in the Porcupine Plateau and on part of the former carbonate platform on the upper Kuskokwim River. The Permian uplift on the Kuskokwim is bordered on the southeast by thick Mississippian and Permian volcanic rocks of the Alaska Range, and on the northwest by Permian volcanic rocks and chert along the Yukon and lower Kuskokwim Rivers. Permian eugeosynclinal ro ks may extend farther north, because Permian terrigenous clastics in the Brooks Range grade southward into chert and argillite, and Permian(?) mafic intrusives occur on St. Lawrence Island.

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