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 Brosge', W.P., Reiser, H.N., Dutro, J.T., Jr., and Detterman, R.L., 1979, Bedrock geologic map of the Phillip Smith Mountains quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-879-B, 2 sheets, scale 1:250,000.
Symbol Kc
Unit name Colville Group
Description Gray to olive-gray; medium bedded to massive quartz arenite to volcanic wacke with interbeds of laminated siltstone and shale, and abundant plant debris and coal fragments; some yellow-weathering very fine grained laminated vitric tuff. Mostly nonmarine. Exposed thickness about 60m.
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