CLASTIC SEDIMENTOLOGY, STRATAL ARCHITECTURE AND PRELIMINARY SEQUENCE STRATIGRAPHIC FRAMEWORK OF UPPER CRETACEOUS SHELF, SHOREFACE, AND FLUVIO-DELTAIC DEPOSITS, SHIVUGAK BLUFFS, NORTH SLOPE OF ALASKA

World-class rock exposures (90 to 120 m high; 11 km long), located at the eastern boundary of the National Petroleum Reserve–Alaska, preserve one of the farthest northern continuous stratigraphic records of the Late Cretaceous (Santonian to Campanian) Arctic Ocean shoreline and coastal plain. This locality, known as Shivugak Bluffs, preserves the interfingering relationship between shelf, shallow marine, and deltaic deposits of the lower Schrader Bluff Formation with the continental fluvial and coastal plain deposits of the Prince Creek Formation. This investigation summarizes the grain size, sedimentary structures, bedform thicknesses, sandbody geometries, ichnology, megafauna, and flora of approximately 630 m (2,067 ft) of measured stratigraphic section at Shivugak Bluffs. Data suggests that this complex Arctic coastline, preserved at Shivugak Bluffs, evolved from wave- and storm-dominated environments to a mainly fluvial-dominated system. Sandbodies at the base of Shivugak Bluffs contain mostly hummocky and swaley cross-stratification, interpreted as prograding wave- and storm-dominated shoreface and/or deltaic deposits, while the upper 200 m (656 ft) of section is interpreted as a muddy, prograding fluvially dominated delta. Preliminary results from high-resolution photography of sandbodies suggest that longshore drift may have played a significant role in controlling coastline morphology. A combination of longshore drift and lobe switching may be mechanisms that helped produce a fluvial-dominated system along a wave-dominated coastline. A 533 m (1,749 ft) thick composite section from Shivugak Bluffs was correlated with publicly available surface and subsurface data to create a dip-oriented cross section between Shivugak Bluffs and the Toolik River area.