Etivluk Group, undivided

Unit symbol: JIPe
Age range Middle Jurassic to Pennsylvanian (323.2 to 168.3 Ma)
Lithology: Sedimentary
Group name: Etivluk Group, undivided
Includes Otuk and Siksikpuk Formations and Imnaitchiak Chert; consists of maroon, red, green, gray, black, and variegated chert and siliceous argillite, minor maroon calcareous siltstone and argillite, and rare maroon or gray limestone lenses (Karl and others, 1989a; Mayfield and others, 1987). Original definition suggested Etivluk Group is present only on allochthonous sheets in the Brooks Range, and not present on autochthonous rock units (Mull and others, 1982). Locally, the Otuk and Siksikpuk Formations are mapped separately as units JTro and TrIPeg

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 JIPcl
Unit name Light-colored cherty unit
Description Thin- to medium-bedded, vitreous to dull, gray, bluish, greenish, olive, reddish, and minor black chert, siliceous claystone, argillite, and siltstone, 100 to 200 m thick. Probably mostly Permian and Triassic in age, equivalent in part to Siksikpuk and Shublik Formations but may contain chert equivalent to part of the Lisburne Group. Unit is approximately equivalent to Early Jurassic Etivluk Group (Mull and others, 1982)
Lithology Sedimentary

Correlated geologic units

Label Pzeg
Description Etivluk Group, undivided: Includes Siksikpuk and Otuk Formations and underlying Immaitchiak Chert
Geologic age Pennsylvanian to Bajocian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Chert < Chemical < Sedimentary Bed Major
Graywacke < Sandstone < Clastic < Sedimentary Carbonaceous Indeterminate, major
Argillite < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Minor
Shale < Mudstone < Clastic < Sedimentary Carbonaceous Minor
Limestone < Carbonate < Sedimentary Bed Incidental