Depositional History of Northern Alaska: ABSTRACT

Abstract

Facies of most rock systems in northern Alaska are related spatially to 4 major structural features: (1) a broad regional high near the north coast, which is a locus of unconformities and of nearshore facies in the upper Paleozoic through lowest Cretaceous rocks, (2) the deep Colville geosyncline between the coast and the Brooks Range, which contains the middle and Upper Cretaceous molasse deposits, (3) a narrow zone of shallow thrusts, the "Disturbed Belt" in front of the End_Page 837------------------------------ Brooks Range, which is the main site of outcrops of Jurassic and Lower Cretaceous orogenic deposits and marks the boundary between distal and nearshore facies in exposed Permian and Triassic rocks, and (4) the Brooks Range overthrust and metamorphic belt, which contains most of the known Devonian and Lower Mississippian molasse deposits, as well as the Devonian carbonates that bordered these deposits on the south, and the upper Paleozoic carbonates that succeeded the molasse deposits. The stratigraphy records Devonian uplift of the northern high, and downwarp of a deep molasse basin on the south; a series of late Paleozoic through earliest Cretaceous marine transgressions onto the northern high from shallow basins on the sites of the present Brooks Range and Colville geosyncline; Late Jurassic to earliest Cretaceous orogeny in the Brooks Range, coupled with downwarp of successive foredeeps that migrated northward with time; the filling of the Colville geosyncline beginning in late Early Cretaceous time; and because the molasse basin was filled from the south and west and was warped in Late Cretaceous time, migration of depocenters through early Tertiary time was northward and northeastward. End_of_Article - Last_Page 838------------