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 Wartes, M.A., Wallace, W.K., Loveland, A.M., Gillis, R.J., Decker, P.L., Reifenstuhl, R.R., Delaney, P.R., LePain, D.L., and Carson, E.C., 2011, Geologic map of the Kavik River area, northeastern Brooks Range, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigation 2011-3A, 14 p., 1 sheet, scale 1:63,360.
Symbol Tsll
Description Light-gray-weathering, fine- to coarse-grained, friable, salt-and-pepper sandstone; commonly trough cross-stratified and locally includes abundant granule- and pebble-rich horizons composed of white vein quartz and dark gray chert clasts. Plant fossil impressions are locally abundant and a prominent hydrocarbon odor is detected in some outcrops, particularly those nearest the Kavik fault. Fine-grained intervals are recessive and generally covered, although limited exposures along the Kavik River include carbonaceous mudstone, coal, siltstone, and thin bentonite seams. Unit is interpreted as dominantly nonmarine fluvial and associated overbank facies. Discontinuously exposed in uplands of the western part of map area between Juniper Creek and the Kavik fault; forms moderately resistant mesa tops covered by large sandstone blocks. Unit is illustrated in well log cross sections by Molenaar and others (1986) and Bird (1999); referred to in Nelson and others (1999) as the lower, unnamed tongue of the Sagavanirktok Formation, where a thickness of 289 m was calculated for the Beli 1 well (north-central part of map) and 385 m for the Canning B-1 well (northeast part of map). Surface exposures were previously referred to as Prince Creek Formation in Reifenstuhl and others (2000) and Mull and others (2003).
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