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Abstract

Cambrian through Middle Devonian fossilifer-ous rocks define three sets of depositional elements in Alaska: (1) a carbonate platform near the craton in the Porcupine Plateau and north of the northeast Brooks Range; (2) shale-chert-volcanic basins south and west of this platform in the Ogilvie Mountains, Yukon-Tanana upland, northeast Brooks Range, and probably along the Arctic coast; and (3) two linear segments of an outer carbonate platform-one trending westward from the southern Brooks Range to Seward Peninsula and St. Lawrence Island, and 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 carbonate beds indicates a Late Devonian orogeny farther north. The regional angular unconformity beneath Mississippian rocks and a Late Devonian granite mark the orogenic belt along the Arctic coast, northeast Brooks Range, and the northern Porcupine Plateau. Upper Devonian turbidite conglomerates also indicate uplift south of the Porcupine Plateau and in the Yukon-Tanana upland.

Mississippian and Pennsylvanian carbonate beds lap northward and eastward from the Brooks Range across a platform of folded Precambrian(?) to Devonian rocks on the Arctic coast and the 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 area. A regional unconformity beneath Permian quarfzose clastic beds indicates other uplifts in the Porcupine Pleateau 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 eugeosyn-clinal rocks may extend farther north, because Permian terrigenous clastic rocks in the Brooks Range grade southward info chert and argillite, and Permiani?) mafic intrusive rocks are present on St. Lawrence Island.

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