Tupik Formation

Unit symbol: Clgt
Age range Pennsylvanian and Upper Mississippian (330.9 to 315.2 Ma)
Lithology: Sedimentary
Group name: Tupik and Kogruk Formations (Lisburne Group)
Uppermost formation of the Lisburne Group in northwestern Alaska; consists primarily of interbedded grayish-black chert, dark- to medium-dark-gray carbonate mudstone, and subordinate greenish-black to dark-greenish-gray chert, and very fine to finely crystalline dolomite (Campbell, 1967). Also includes dark-gray to black, micritic, silty, mostly thin-bedded, very finely crystalline to microcrystalline limestone with thin chert interbeds. Sable and Dutro (1961) report a sparse fossil fauna that includes Mississippian sponge spicules and cephalopods and Late Mississippian foraminifers. Upper part of formation is missing at type section. Campbell (1967) geographically extended formation to the Point Hope quadrangle and speculated that the “absence of fauna of Pennsylvanian age contributes to interpretation of disconformity with overlying Siksikpuk; on other hand, no fossils have been found at higher stratigraphic position than about 150 ft [45 m] below top; it is possible that Pennsylvanian Period is represented by rather thin zone of nonfossiliferous rocks.” Unit is 100–200 m thick (Sable and others, 1984a, b, c). Base is gradational with the Kogruk Formation (Curtis and others, 1984; Mayfield and others, 1984; Ellersieck 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 Mld and KJm
Unit name Lisburne Group, dark-colored facies and Mafic igneous rocks, undivided
Description Locally distinguished black to dark-gray limestone, claystone and chert. As much as 400 m thick. Resembles Tupik Formation but locally contains more abundant claystone and thicker chert beds. Also includes rocks of unit KJm, Dark-grayish-green to dark-gray gabbro, diabase, basalt, microgabbro, and minor diorite; locally includes some pillow, pillow-layer, or flow structures.
Lithology Sedimentary

Correlated geologic units

Label Mlt
Description Lisburne Group, Tupik Formation, uppermost unit in western Alaska
Geologic age Mississippian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Chert < Chemical < Sedimentary Bed Major