Nuka Formation

Unit symbol: IPMn
Age range Carboniferous (330.9 to 298.8 Ma)
Lithology: Sedimentary
Group name: Nuka Formation
Medium-gray, light-gray-weathering, arkosic limestone and sandstone, and interbedded black clay shale. Sandstone is fine- to medium-grained and calcareous, in thickening- and coarsening-upward beds; section has turbidite characteristics with graded beds up to 1 m thick and has convolute bedding and large flute casts at the base of some beds; base of section is dominantly black clay shale. Contains locally abundant glauconite and rare hematite-cemented beds. Depositional thickness is estimated to range from a few meters to as much as 300 m (Dover and others, 2004). Crinoids and brachiopods of Late Mississippian to Early Pennsylvanian age are conspicuous fossils in scattered localities (Mayfield and others, 1987; Mull and others, 1994). Also contains Late Mississippian foraminifers (Sable and others, 1984a, b, c; Mayfield and others, 1987) and Early Pennsylvanian conodonts (Curtis and others, 1984)

Source map information

Source map Sable, E.G., Dutro, J.T., Jr., Morris, R.H., and Tailleur, I.L., 1984, Geologic map of the eastern Kukpowruk-Nuka Rivers region, northwestern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1671, 2 sheets, scale 1:63,360.
Symbol IPMn
Unit name Nuka Formation
Description Very distinctive light-hued, gray and greenish, arkosic, calcarenitic, and glauconitic marine sandstone and conglomerate, intimately associated limy siltstone, platy limestone, sandy dolomite, dark claystone, and mostly light-colored unit. Likely only a few hundred m thick.
Lithology Sedimentary

Correlated geologic units

Label IPMn
Description Nuka Formation
Geologic age Mississippian to Pennsylvanian
Geologic setting Undivided
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Arkose < Sandstone < Clastic < Sedimentary Calcareous Major