Paleoenvironmental Reconstruction of A Late Cretaceous, Muddy, River-Dominated Polar Deltaic System: Schrader Bluff–Prince Creek Formation Transition, Shivugak Bluffs, North Slope of Alaska, U.S.A.

Abstract

Upper Cretaceous (Santonian to late Campanian) strata from the upper 196 m at Shivugak Bluffs along the Colville River of northern Alaska preserve a paleopolar, fluvial-deltaic succession deposited along a prograding paleo-Arctic Ocean coastline. The uppermost lower Schrader Bluff Formation is best classified as a river-dominated delta based on muddy prodelta and delta-front deposits that contain abundant hyperpycnites, subaqueous terminal distributary channels, interdistributary bays, and mouth bars. This deltaic succession is overlain by distal distributaries and a braided fluvial system of the Prince Creek Formation. Channel measurements and paleo-discharge calculations from Prince Creek Formation distributaries indicate that rivers were the appropriate size and had the appropriate discharge to regularly produce hyperpycnites. Delta front and interdistributary bays transitioned into lakes and floodbasins on the lower delta plain, alongside distributary channels during delta lobe reorganization and abandonment. These floodbasins were subsequently transgressed and are overlain by proximal shelf and prodelta muds containing Phycosiphon. Overlying strata containing delta front, interdistributary bay, terminal distributary channel, distributary mouth bar, and distributary channel deposits signaled the reactivation of the delta lobe. Ultimately, these deltaic environments were incised into and became overlain by braided channel deposits during a marked drop in relative sea level and progradation of the fluvial system. Combining ichnologic and sedimentologic observations was critical to identify eleven distinct deltaic and continental paleoenvironments. This study documents the architecture and evolution of an ancient, high-latitude, muddy, river-dominated deltaic system and highlights the autogenic and allogenic processes preserved in the system.

Geologic map of the Umiat-Gubik area, central North Slope, Alaska

“…Sigma-1 is the maximum principal stress direction; sigma-3 is the minimum principal stress direction; principle stress arrows depicted here are not quantitative vectors. Figure modified from Christie-Blick and , Sylvester (1988), and Twiss and Moores (1992); see also McClay (1987). and there are no wholly repeated fracture set patterns among the stereonet plots of figure 9although there are several fracture sets that occur at more than one locality.…”

An Early Permian, paleopolar, postglacial, river-dominated deltaic succession in the Mackellar–Fairchild formations at Turnabout Ridge, Central Transantarctic Mountains, Antarctica

“…6A) are interpreted as suspension deposits of hypopycnal plumes (Bhattacharya and MacEachern, 2009). Distal-delta-front deposits in FA-I tend to contain thicker and more frequent sandstone beds than prodelta deposits, however, those sandstones are thinner and less common than sandstone found along the proximal-delta-front (FA-III) (Fielding, 2010;Hurd et al, 2014, van der Kolk et al, 2015.…”

Upper Cretaceous and Lower Jurassic strata in shallow cores on the Chukchi Shelf, Arctic Alaska

“…The Wrangel-Herald Arch thrust belt is the relict northern leading edge of the Chukotka orogen. The thrust belt is overprinted by the South Chukchi-Hope successor basin, which is bounded by Cenozoic transtensional faults and filled with Eocene and younger strata (Tolson, 1987;Klemperer and others, 2002;Verzhbitsky and others, 2012). Sherwood and others (2002) and Craddock and Houseknecht (2016).…”

“…1) and likely includes pre-Brookian rocks sub-cropping the unconformity on the Herald Arch. Strata above the unconformity represent the northern edge of the Hope Basin, which is filled by Eocene and younger strata (Tolson, 1987;Verzhbitsky and others, 2012).…”