Sagavanirktok Formation

Unit symbol: Tsf
Age range Tertiary, Miocene to Paleocene (59.2 to 3.6 Ma)
Lithology: Sedimentary
Group name: Sagavanirktok Formation
Mostly nonmarine, poorly consolidated siltstone, sandstone, conglomerate and lignite of the North Slope of Alaska and present only east of the Colville River. Divided into four members, in descending stratigraphic order: Nuwok, Franklin Bluffs, White Hills, and Sagwon Members. Unit consists of northeasterly prograding, upward-fining sequences that have basal fluvial conglomerate and coarse sandstone grading to mudstone that is commonly bentonitic and contains lignite (Mull and others, 2003). Mull and others (2003) revised the original definition of the Sagwon Member to exclude the lower coal-bearing beds at Sagwon Bluffs (informal name for bluff located along Sagavanirktok River opposite the Sagwon airstrip in the central Sagavanirktok quadrangle), concluding that they more properly belong to the Prince Creek Formation; they defined the base of the Sagwon Member—and therefore the base of the Sagavanirktok Formation—as a white-weathering sandstone and conglomerate that caps ridges in the northern Brooks Range foothills. Conglomerate clasts are generally white quartz, black chert, and light-gray quartzitic sandstone and minor pale-green chert. Sagwon Member is late Paleocene in age (Mull and others, 2003). White Hills Member is lithologically similar, but the finer-grained upper part is poorly exposed. Conglomerate clasts are generally gray quartzitic sandstone, white quartz, black chert, and leached light-gray siliceous tuff and lesser gray to pale-green and maroon to red chert. Its age is considered late Paleocene to early Eocene. Franklin Bluffs Member definition was also revised by Mull and others (2003); its lower part consists of white- to pink-weathering, poorly consolidated sandstone and conglomerate; conglomerate clasts are predominantly black chert and lesser white and gray quartz. Its upper part, generally not exposed and primarily known from well data, consists of poorly consolidated thin-bedded mudstone and siltstone. Age is probably early Eocene to Miocene (Mull and others, 2003) and the fauna suggests a nearshore or estuarine environment. The Nuwok Member is only exposed in northeastern Alaska and consists of unconsolidated pebbly sandstone or conglomerate overlain by pebbly mudstone (Detterman and others, 1975). Its age is late Miocene to Pliocene and character of the sediments and fauna suggest a nearshore or beach environment. In the Harrison Bay quadrangle, Carter and Galloway (2005) report a Paleocene map unit (Tsg) assigned to the Sagavanirktok Formation where “* * * deposits consist of moderately to poorly consolidated conglomerate, sand, gravelly sand, and pebbly shale with thin coal beds and locally common lignitized logs”

Source map information

Source map Gillis, R.J., Decker, P.L., Wartes, M.A., Loveland, A.M., and Hubbard, T.D., 2014, Geologic map of the south-central Sagavanirktok Quadrangle, North Slope, Alaska: Alaska Division of Geological & Geophysical Surveys Report of Investigation 2014-4, 24 p., 2 sheets, scale 1:63,360. doi:10.14509/29138
Symbol Tsw
Description Poorly consolidated, white-weathering pebble to boulder conglomerate and pebbly sandstone that form excellent outcrops in the lower part of the White Hills Member at a meander bend on the Toolik River a few hundred meters north of the northern map boundary. These exposures were designated by Mull and others (2003) as the reference section for the basal White Hills Member to supplement observations at the type section located in the northwestern White Hills. Clasts include light brownish-gray quartzite; black, brown, gray, light green, tan, and cream-colored chert; vein quartz; common white to beige leached tuff; deeply altered plutonic or gneissic rocks; local cobbles and boulders of quartz–mica schist; and local concentrations of fusain (charcoal) clasts. The quantity of volcanic clasts and the presence of plutonic and metamorphic clasts distinguish conglomerate of the White Hills Member from older conglomeratic units. Pebbles and cobbles greatly outnumber boulders. Conglomerates are dominated by low- to high-angle cross-stratification in beds up to 1 m (3 ft) or more in thickness, amalgamated to thicknesses exceeding 10 m (33 ft). Sandstones associated with the conglomerates form lenticular bodies with steeply dipping cross-stratification that suggests generally east-directed currents. Bedding is locally marked by concretionary beds of sideritized mudstone, which also occurs as rare, angular clasts up to boulder size in the conglomerates; this observation is consistent with scour and remobilization of early-formed siderite, and high-capacity flow events. The lower contact is not exposed, but is thought to be a sequence boundary (Mull and others, 2003) with the basal conglomeratic beds overlying bentonitic mudstone, lignite, and clinkers of the upper part of the Sagwon Member (Tss). Brown-weathering silty mudstones containing thin, discontinuous lignite beds are exposed below the sharp, apparently unconformable upper contact south of Franklin Bluffs. Thickness of the White Hills Member is not constrained by outcrop information; Mull and others (2003) estimated it may be as thick as 800 m (~2,600 ft). The late Paleocene (?) to early Eocene age inferred by Mull and others (2003) is based on palynological data in the underlying Sagwon Member in the eastern White Hills, and from the top of the member in the Franklin Bluffs area (Frederiksen and others, 1996).
Lithology Sedimentary

Correlated geologic units

Label Tswh
Description Sagavanirktok Formation, White Hills Member
Geologic age Late-Paleocene to Early-Eocene
Geologic setting Sedimentary, continental
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Major
Quartzose-sandstone < Sandstone < Clastic < Sedimentary Bed Indeterminate, major