INTO THE FOREDEEP: PROVENANCE SHIFTS AND REGIONAL TRENDS DURING THE EARLY CRETACEOUS EVOLUTION OF THE ARCTIC ALASKA COLVILLE FORELAND BASIN

The Colville Foreland Basin of Arctic Alaska is a product of collision of the Jurassic Koyukuk arc and continental Arctic Alaska terrane during the assembly of the northern Cordillera. In this study, we discuss spatiotemporal provenance trends to understand the evolution of the Colville Foreland Basin. We present new detrital zircon U-Pb (DZ) data from ~100 samples of Lower Cretaceous strata from the North Slope and use a mixture modeling approach to interpret sources of sediment based on previously published data.

Results show that the northward retrograding transgressive system comprising the Hauterivian Kemik Sandstone and informal pebble shale unit is dominated by Paleozoic–Neoproterozoic ages that are interpreted to have been derived from the Arctic Alaska terrane during early foreland subsidence. To the southwest, flysch and mélange of the Neocomian Okpikruak Formation that record the first pulse of sediment shed northward into the ancestral foredeep have distinct Jurassic DZ ages that have been attributed to Angayucham and Koyukuk provenance. The Aptian–Cenomanian wedgetop facies of the Fortress Mountain Formation, deep basin facies of the lower Torok Formation, and the northern extent of the Nanushuk-Torok Clinothem (NTC) are dominated by Permian–Early Cretaceous DZ ages that indicate Russian Chukotka provenance. Conversely, Paleozoic and older zircon are abundant within the southern ~70–90 km of the NTC and suggest that central Brooks Range sediment was sequestered within the proximal foredeep and less broadly distributed to the north. Stratigraphic transects show an upsection decrease in Chukotka sediment and near absence in upper Nanushuk Formation non-marine topsets. This spatial and temporal transition delineates the northeastward propagation of the foredeep axis during progradation of the NTC. East of the Nanushuk ultimate shelf margin, sand-rich terminal lowstand deposits are dominated by central Brooks Range sediment and are overlain by a sediment starved interval in the eastern foredeep. The subsequent transgressive Ninuluk Sandstone marks a return of minor quantities of Chukotka sediment, suggesting that transgressive systems both rework older strata and efficiently mix shelfal sediment. Ongoing DZ work in the Colville Basin will explore provenance shifts in subsequent Cretaceous–Cenozoic clinothems and wedgetop basin development.