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 Keller, A.S., Morris, R.H., and Detterman, R.L., 1961, Geology of the Shaviovik and Sagavanirktok Rivers region, Alaska, in Exploration of Naval Petroleum Reserve No. 4 and adjacent areas, northern Alaska, 1944-1953, Part 3, Areal Geology: U.S. Geological Survey Professional Paper 303-D, p. 169-222, 6 plates, scale 1:63,360.
Symbol Ts
Unit name Sagavanirktok Formation
Description In the northeastern part of the mapped area, the formation crops out in broad plunging anticlines and synclines. The more resistant sandstone and conglomerate form ledges and whaleback ridges on the limbs of the structures between the Kavik and Shaviovik Rivers. The best exposures of the formation are in the interstream area between Fin Creek and the Shaviovik River, where the rocks form the south flank of the Shaviovik anticline, and in cutbanks along Fin Creek. The formation is overlain by flat-lying Tertiary and Quaternary deposits along the present stream flood plains, terraces, and hillsides. The formation consists of nonmarine to beach-type sediments consisting of poorly consolidated conglomerate, sandstone, and siltstone with interbeds of shale and coal
Lithology Sedimentary

Correlated geologic units

Label Tsg
Description Sagavanirktok Formation
Geologic age Late-Paleocene to Zanclean
Geologic setting Sedimentary, undivided
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Indeterminate, major
Conglomerate-sandstone < Mixed-clastic < Clastic < Sedimentary Bed Indeterminate, major
Mudstone < Clastic < Sedimentary Bed Indeterminate, major
Sandstone < Clastic < Sedimentary Bed Indeterminate, major
Lignite < Coal < Sedimentary Bed Incidental