Sedimentology and sequence stratigraphy of the Cretaceous Nanushuk, Seabee, and Tuluvak formations exposed on Umiat Mountain, north-central Alaska

Abstract

Upper Cretaceous strata of the upper part of the Nanushuk Formation, the Seabee Formation, and the lower part of the Tuluvak Formation are exposed along the Colville River on the east flank of Umiat Mountain in north-central Alaska. The Ninuluk sandstone, which is the uppermost unit of the Nanushuk Formation, displays a vertical succession of facies indicative of deposition in an upward-deepening estuarine through shoreface setting. A marine-flooding surface lies between the Ninuluk sandstone and organic-rich shale of the basal part of the Seabee Formation. The Ninuluk sandstone and the lower part of the Seabee Formation are interpreted as components of a transgressive-systems tract. The lowest, well-exposed strata in the Seabee Formation are a succession of shoreface sandstone beds in the middle of the formation. Integration of outcrop information and the Umiat No. 11 well log suggests that this sandstone succession rests on a sequence boundary and is capped by a marineflooding surface. The sandstone succession is interpreted as a lowstand-systems tract. The upper part of the Seabee Formation includes a thick interval of organic-rich shale deposited in a dysaerobic offshore environment, and the gradational Seabee-Tuluvak contact is a coarsening-upward shale-to-sandstone succession deposited in a prodelta/delta-front environment. The observation that the upper part of the Seabee Formation correlates with seismic clinoforms suggests that dysaerobic conditions extended well up onto the prodelta slope during intervals of transgression and highstand. Correlation of the Umiat Mountain outcrop section with well logs and seismic data suggests that sequence boundaries and lowstand shoreface deposits may be common in the Seabee Formation and that wave action may have been important in transporting sand to the paleoshelf margin. These conclusions may contribute to an enhanced understanding of sand distribution in prospective lowstand turbidite deposits in the subsurface of the central North Slope of Alaska.

Geologic framework for the national assessment of carbon dioxide storage resources: Alaska North Slope and Kandik Basin, Alaska

“…To the east, conglomerates fine and interfinger with coal, shale, and compositionally and texturally mature sandstone. Near the eastern limit of the Tuluvak, it consists of fine-to medium-grained quartz arenite with low-angle cross bedding and various marine fossils (Mull and others, 2003;Houseknecht and Schenk, 2005). The Tuluvak was deposited in a variety of depositional environments, and generally following regional grain-size trends, depositional facies tend to transition from nonmarine in the west to shallow marine in the east (Mull and others, 2003).…”

“…3) is a succession of continental slope and basin-floor strata that was deposited throughout the Late Cretaceous and Tertiary, during the later stages of the Brookian orogeny (Moore and others, 1994;Decker, 2007Decker, , 2010; also see Houseknecht and Schenk, 2005). The formation primarily consists of mudstone that accumulated downdip from the Upper Cretaceous to Neogene continental shelf successions of the Prince Creek, Schrader Bluff, and Sagavanirktok Formations (Decker, 2007(Decker, , 2010; also see Houseknecht and Schenk, 2005).…”

“…The SAU spans depths of 3,000 to 5,200 ft and an area of 798,000 acres (±10 percent). A combination of data was used to constrain the structural architecture of the unit, including a database of 89 borehole penetrations (Kenneth Bird, USGS, written commun., 2007), stratigraphic correlations across the central North Slope (Decker, 2007(Decker, , 2010, and regional seismic lines (for example, see Houseknecht and Schenk, 2005). In general, the formation dips at a low angle to the east across the central North Slope, and the SAU achieves its maximum depth along its eastern edge.…”

“…3) consists of continental slope and basin-floor strata that were deposited downdip of the Tuluvak continental shelf as depositional systems prograded across the Colville Basin during the Cenomanian to Coniacian (Bird and Molenaar, 1992;Moore and others, 1994;Mull and others, 2003;Houseknecht and Schenk, 2005). Similar to the Tuluvak Formation, the Seabee is confined to the central part of the Alaska North Slope region, and in general, it consists of mudstone, silty mudstone, and medium-to dark-gray to black, fissile, organic-matter-rich shale interbedded with thin tephras (Mull and others, 2003).…”

“…3) is a succession of continental slope and basin-floor strata that was deposited throughout the Late Cretaceous and Tertiary, during the later stages of the Brookian orogeny (Moore and others, 1994;Decker, 2007Decker, , 2010; also see Houseknecht and Schenk, 2005). The formation primarily consists of mudstone that accumulated downdip from the Upper Cretaceous to Neogene continental shelf successions of the Prince Creek, Schrader Bluff, and Sagavanirktok Formations (Decker, 2007(Decker, , 2010; also see Houseknecht and Schenk, 2005). However, regional subsurface correlation of gamma ray, spontaneous potential, and resistivity logs indicate the presence of relatively coarse-grained lobes of material draped above the toes of several continental slope successions, and the stratigraphic context of these beds suggests that they are submarine slope-apron and (or) basin-floor fan-turbidite complexes (Decker, 2007(Decker, , 2010.…”