NEW CONSTRAINTS ON THE EVOLUTION OF LATE CRETACEOUS DEPOSITIONAL SYSTEMS IN THE COLVILLE FORELAND BASIN, EAST-CENTRAL NORTH SLOPE, ALASKA

The northern Brooks Range foothills of Alaska’s east-central North Slope present an excellent opportunity to examine the influence of tectonic and eustatic processes on the evolution of foreland basin stratigraphy. In particular, this area allows for the integration of detailed outcrop observations with nearby well and 2-D seismic data. Recent field and subsurface studies of Upper Cretaceous strata in the Sagavanirktok Quadrangle have resulted in a revised formation nomenclature that emphasizes regional sequence stratigraphic relationships. These strata record the time-transgressive northeastward progradation of genetically related shelf, slope and deep water facies. In these rocks, we have found that the stratigraphic record of major rises in relative sea level (e.g. condensed sections) can be readily recognized and provide a useful criteria for subdividing depositional cycles and correlating across widely disparate parts of the basin. We recognize flooding surfaces and episodes of sediment starvation associated with significant landward shifts in the paleoshoreline in the Cenomanian-Turonian, Santonian, and middle Campanian. In an effort to improve stratigraphic correlations, we have utilized a number of tools including megafossil biostratigraphy, palynology, chemostratigraphy, and sandstone composition, each with varying degrees of success. Most recently, we successfully generated U-Pb zircon ages from several airfall volcanic units using the LA-ICP-MS technique. Upper Cretaceous condensed intervals are typically shale-prone and preserve abundant and thick silicified tuff and bentonite zones, suggesting this method holds promise in future chronostratigraphic studies. The improved resolution offered by U-Pb geochronology will not only allow us to test existing stratigraphic correlations within the basin, but also assess the impact of eustatic sea level rises on the stratigraphic architecture of northern Alaska.