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 Tss
Description Poorly consolidated light gray to white, locally pink–orange-weathering pebble to cobble conglomerate, medium-grained to pebbly sandstone, siltstone, claystone, and coal. Quartzose and chert-rich sandstones and conglomerates dominate the base of the member at the type section in the area of VABM Gard at Sagwon Bluffs on the Sagavanirktok River. Clasts consist mainly of vein quartz, black to gray fresh chert, white tripolitic chert, and light gray quartzitic sandstone, with subordinate varicolored chert. Low-angle scour-and-fill stratification is pervasive in crudely-defined conglomerate beds 20–50 cm (8–20 in) thick, amalgamated into packages 3–10 m (10–33 ft) thick. Conglomerates are interspersed with and truncate local beds of trough cross-stratified, medium-grained to conglomeratic sandstone up to 50 cm (20 in) thick. Collectively the basal interval is interpreted as braided fluvial deposits. Discontinuous outcrops in cutbanks of the Toolik River in the northwestern part of the map area appear to extend higher in the stratigraphic section and contain larger proportions of sandstone and finer-grained lithologies. Well developed stream-scale channels, sigmoidal cross-bedded sandstone, planar cross-stratified conglomerate, and thin- to medium-bedded sandstone, siltstone, carbonaceous mudstone, and local coal in this part of the Sagwon Member are considered likely to have been deposited by meandering fluvial systems. As revised by Mull and others (2003), the basal contact of the Sagwon Member is a sharp, apparently unconformable surface separating the overlying white-weathering conglomerates from the underlying coal, bentonite, carbonaceous mudstone, siltstone, and light-olive- to tan-weathering salt-and-pepper sandstone of the Prince Creek Formation. Thickness of the Sagwon Member is unknown from outcrop data; Mull and others (2003) speculated it may exceed 900 m (2,950 ft). Tentative picks in the Bush Federal 1 well correspond to a thickness of 220 m (722 ft) in the measured depth interval ~832–612 m (~2,730–2,008 ft) (fig. 4). The late Paleocene(?) age of the Sagwon Member as revised by Mull and others (2003) is based on palynological data in the eastern White Hills reported by Frederiksen and others (1996).
Lithology Sedimentary

Correlated geologic units

Label Tss
Description Sagavanirktok Formation, Sagwon 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 Major
Mudstone < Clastic < Sedimentary Calcareous Indeterminate, major