Tuluvak Formation

Unit symbol: Ktu
Age range Upper Cretaceous, Coniacian to upper Turonian (93.9 to 86.3 Ma)
Lithology: Sedimentary
Group name: Nonmarine to shelf sedimentary rocks
Fine- to coarse-grained to granular sandstone and quartz- and chert-pebble conglomerate occur in several relatively resistant intervals, some of which consist of conspicuously well-rounded and well-sorted pea gravel with no interstitial matrix. Lower part typically medium- to coarse-grained, well-sorted sandstone. Clasts are dominantly quartz and chert, and the sandstone is interbedded with bentonite, bentonitic shale, carbonaceous shale, and coal. Upper part of unit dominantly fine-grained sandstone. In southwest part of exposure area, formation is thicker and contains more resistant sandstone and conglomerate; to the east and northward, formation thins and becomes finer grained as it transitions from nonmarine braided-stream deposits to marine sandstone. Forms prominent bluffs along the north and northwest side of the Colville River downstream from Umiat, and scattered exposures along the Chandler and Anaktuvuk Rivers. Mudstone, siltstone, and shale are end members of a continuum of lithologies that are typically medium- to dark-gray, fissile in parts, and bentonitic in parts. Conglomerate is locally found in basal part of unit and consists of well-rounded pebbles of white to light-gray quartz, quartzite, and medium- to dark-gray chert and has a sandstone matrix and quartz cement. Sandstone, siltstone, and shale of upper part of unit are poorly exposed; sandstone is gray, probably mostly quartz and chert and prominently cross-bedded, siltstone and shale are gray and brownish gray and poorly indurated. Tuff beds, coal, and ironstone are found locally (Kelley, 1990a). Unit defined by Gryc and others (1951), Whittington (1956), and Brosgé and Whittington (1966) as part of Prince Creek Formation and elevated to formation status by Mull and others (2003). Redefined unit also contains the now abandoned Ayiyak Member of the Seabee Formation. Lower part of unit interfingers with the Seabee Formation (D.W. Houseknecht, USGS, written commun., 2014)

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 Kpcl
Description Light brown-, tan-, to buff-weathering very-fine- to fine-grained, salt-and-pepper textured sandstone, conglomerate, dark brown to black carbonaceous mudstone, thin coal beds, tuffaceous siltstone, bentonite, and tuff. Rocks are dominantly nonmarine and similar to the main part of the Prince Creek Formation (TKpc), but occur stratigraphically beneath the upper Schrader Bluff map unit (Ksbu) and overlie and intertongue with the middle Schrader Bluff map unit (Ksbm). The unit is distinguished from adjacent Schrader Bluff Formation by the brownish color, presence of conglomerates, coaly beds, fossil wood, leaves, and carbonaceous debris, and the absence of marine megafossils, marine ichnofossils, and wave-influenced sedimentary structures. In the map area, the lower tongue of the Prince Creek Formation is only exposed in intermittent ribs along the Toolik River on the flanks of the Kuparuk and Aufeis anticlines, where local interfingering with marine facies of the middle Schrader Bluff Formation is observed at sub-mappable scales. Thickness of the unit is probably at least 250 m (820 ft) (P. Flaig and D. van der Kolk, oral communication, 2009) where measured on the south flank of the Kuparuk anticline on the west side of the Toolik River. The age of the lower tongue of the Prince Creek Formation in the map area is bracketed as Campanian by palynomorph ages from the overlying upper Schrader Bluff Formation on the Toolik River (Molenaar and others, 1984) and in the Canning Formation (Kc) underlying laterally equivalent strata of the middle Schrader Bluff map unit (Ksbm) on Sagashak Creek (LePain and others, 2008b). U/Pb analyses (results pending) from closely associated bentonite and tuff beds may yield more precise age constraints.
Lithology Sedimentary

Correlated geologic units

Label Ktu
Description Tuluvak Formation, formerly tongue of Prince Creek Formation (includes Ayiyak Member of Seabee Fm.)
Geologic age Turonian to Coniacian
Geologic setting Sedimentary, deltaic-and-nearshore
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Major
Quartzose-sandstone < Sandstone < Clastic < Sedimentary Bed Major