Noatak Sandstone

Unit symbol: Degn
Age range Upper Devonian (382.7 to 358.9 Ma)
Lithology: Sedimentary
Group name: Noatak Sandstone (Endicott Group)
Gray to greenish-gray, medium-bedded quartzose sandstone, generally fine-grained, calcareous, finely micaceous, probably more than 500 m thick; contains abundant yellow-orange limonitic spots and commonly contains conspicuous cross beds and ripple marks; beds are up to 2 m thick and interbedded with gray silty micaceous shale and, locally, with thin silty limestone. Locally contains massive, thick-bedded, white to light-gray-weathering pebble conglomerate, which contains matrix-supported white quartz and black and gray chert pebbles to 2 cm diameter. Unit was mostly deposited on a marine shelf (Mull and others, 1994). Conformably overlies Hunt Fork Shale. Conformably underlies Ear Peak Member of the Kanayut Conglomerate). Thickness ranges 0 to 560 m. Contains late Late Devonian (middle Famennian) marine megafossils, including brachiopods, gastropods, pelecypods, and echinoderms, and trace fossils such as Skolithos (Nilsen and others, 1985). As mapped here, includes a unit informally described as wacke sandstone and quartzite members of the Hunt Fork Shale (Nelson and Grybeck, 1980; Brosgé and others, 1979). This unit was described as grayish green, brown, and black micaceous manganiferous clay shale and shaly siltstone that contains interbedded thin- to medium-bedded, fine- to medium-grained, limonitic quartzitic quartz-chert wacke that weathers orange and brown; green fine-grained wacke; and minor amounts of gray quartzite and calcareous sandstone. Wacke is composed of fragments of quartz, chert, muscovite and biotite schist, and minor amounts of plagioclase feldspar. Ferruginous lenses contain brachiopod coquina and pebbles of chert and shale and ironstone (Brosgé and others, 1979; Kelley, 1990a). Nelson and Grybeck (1980) reported brachiopods, gastropods, pelecypods, echinoderms, other mollusks, plants, feeding tracks, and trails. Brosgé and others (2000) mapped dark-gray wacke and brown calcareous sandstone containing coquina lenses as part of this unit. As mentioned above, unit is much more widely exposed than shown here because it is commonly mapped as a unit within the Kanayut Conglomerate

Source map information

Source map Mull, C.G., and Werdon, M.B., 1994, Generalized geologic map of the western Endicott Mountains, central Brooks Range, Alaska: Alaska Division of Geological and Geophysical Surveys Public-Data File 94-55, 1 sheet, scale 1:250,000.
Symbol Dn
Unit name Allochthonous Rocks, Endicott Mountains Allochthon, Key Creek and Ivotuk Hills sequences, undivided; Noatak Sandstone
Description Light-gray to light-brown, fine- to coarse-grained, thick-bedded sandstone and quartzite in units up to 29 m thick; interbedded with dark-gray to brown shale with ironstone nodules; sandstone commonly crossbedded, contains scattered limonitic spots. Upper part generally forms steep tan-weathering rubble-covered mountain slopes, becomes thinner down section
Lithology Sedimentary

Correlated geologic units

Label Dnu
Description Endicott Group, Noatak Sandstone and phyllite, carbonate and clastic rocks of the Nakolik River, shale,
Geologic age Late-Devonian to Devonian
Geologic setting Sedimentary, shallow-marine-siliciclastic
Lithology Form Importance
Sandstone < Clastic < Sedimentary Calcareous Major
Black-shale < Shale < Mudstone < Clastic < Sedimentary Calcareous Minor
Siltstone < Clastic < Sedimentary Calcareous Minor
Limestone < Carbonate < Sedimentary Bed Incidental