CONTRASTING CRETACEOUS PALEODRAINAGE SYSTEMS OF BASINS FLANKING THE BROOKS RANGE, ARCTIC ALASKA

Processes such as tectonic uplift, erosional denudation, sediment transport and dispersal have direct implications on the evolution of synorogenic sediment routing. As observed in several active Cenozoic orogens, differences in sedimentary filling patterns are recognizable by variations in large-scale axial and transverse river systems versus smaller tributaries observed draining into and within the basins separated by orogenic highs. These variations in drainage systems can lead to differences in provenance signatures recorded by the basin sediments that can be used to aid in reconstructing and understanding the paleodrainage history of inactive orogens. In northern Alaska, the Brooks Range (BR) is flanked by two major sedimentary basins, the northern Colville foreland basin (CB) and southern Yukon Koyukuk Basin (YKB). Deposition of thick successions of clastic rocks in the CB occurred synchronously with the formation of YKB. To the north in the CB, sediments derived from the west from Russia longitudinally filled the basin (Moore et al., 2015), while deposition in the YKB was most likely derived from more local sources. Our generalized stratigraphy of the northern Kobuk Koyukuk sub-basin (KKB) of the YKB, combined with provenance results, U-Pb and Lu-Hf isotopes of detrital zircons reflect the tectonic and erosional unroofing of the adjacent orogenic highlands. U-Pb ages of detrital zircons collected from the lowest mafic-rich sediments yield maximum depositional ages (107 Ma) that reflect initial erosion of the structurally highest Angayucham terrane of the BR and also the formation of the basin by at least the late E. Cretaceous. Detrital zircons ages and Hf isotopes indicate that sediments of the KKB were sourced proximally from the southern Brooks Range and Ruby terrane. Sediments eroded from the adjacent metamorphic highlands were transported to the KKB by a system of small drainages that locally filled the basin. Differences in detrital zircon signatures between similar age strata in the CB and the KKB suggest that the sediments were fed into the basins by two contrasting drainage systems (large-scale axial transport in the CB vs. local tributaries in KKB) from entirely different source areas. This interpretation indicates that the BR acted as a drainage divide during late Early Cretaceous deposition.