Endicott Group, undivided

Unit symbol: MDe
Age range Mississippian to Devonian (419.2 to 323.2 Ma)
Lithology: Sedimentary
Group name: Endicott Group, undivided
Clastic sequence that consists of seven formally defined Formations. Herein, also includes the informally defined Ulungarat formation of Anderson (1991a) at its base. Typically composed of shale, sandstone, and conglomerate (Tailleur and others, 1967). Extends throughout the Brooks Range and also known in the subsurface of the North Slope. As shown here, represents undifferentiated parts of the Endicott Group. Defined unit age extends into the Early Permian, however, Pennsylvanian and Permian rocks of the unit are not exposed at the surface and only known from the subsurface of the North Slope. The Mississippian Itkilyariak Formation of Mull and Mangus (1972) is the uppermost formation of the Endicott Group in Sadlerochit Mountains of the northeast Brooks Range. There it overlies the undivided Kayak Shale and Kekiktuk Conglomerate. The Itkilyariak Formation consists of red and maroon sandstone, conglomerate, breccia, and limestone interbedded with maroon and greenish-gray shale and light-gray quartzitic sandstone about 45 m thick. Extent of unit is not mapped but, according to Mull and Mangus (1972), unit unconformably overlies undated and unnamed shale and sandstone at its type locality, and in some areas, overlies—unconformably or gradationally—undivided Kayak and Kekiktuk Formations. The Itkilyariak Formation gradationally underlies the Alapah Limestone (unit Mlga) of the Lisburne Group. Age is Late Mississippian based on biostratigraphic dating of early Late Mississippian fauna. Armstrong and Bird (1976) described the Itkilyariak Formation as part of a transgressive depositional suite of Carboniferous rocks of Arctic Alaska and proposed that redbeds and evaporites in the formation may represent a slowing in rate of transgression, perhaps reflecting local progradation and development of mudflats and (or) change of climate from humid to arid. On the Lisburne Peninsula between Cape Thompson and Cape Dyer, the Endicott Group consists of (ascending) the informal Mississippian Kapaloak sequence (marine and fluvial) and an unnamed Upper Mississippian (marine) shale (Moore and others, 1984)

Source map information

Source map Karl, S.M., Dumoulin, J.A., Ellersieck, Inyo, Harris, A.G., and Schmidt, J.M., 1989, Preliminary geologic map of the Baird Mountains and part of the Selawik quadrangles, Alaska: U.S. Geological Survey Open-File Report 89-551, 65 p., 1 sheet, scale 1:250,000.
Symbol MDe
Unit name Endicott Group, undivided
Description Unit includes the Hunt Fork Shale, Noatak Sandstone, Kanayut Conglomerate, Kekiktuk Conglomerate, and Kayak Shale.
Lithology Sedimentary

Correlated geologic units

Label MDe
Description Endicott Group, undivided. Unit includes the Itkilyariak Formation, Kekiktuk Conglomerate, Kayak Shale, Kanayut Conglomerate, Noatak Sandstone, Kurupa Sandstone, and Hunt Fork Shale
Geologic age Devonian to Mississippian
Geologic setting Undivided
Lithology Form Importance
Conglomerate-mudstone < Mixed-clastic < Clastic < Sedimentary Bed Major
Conglomerate < Clastic < Sedimentary Bed Indeterminate, major
Shale < Mudstone < Clastic < Sedimentary Bed Indeterminate, major
Sandstone < Clastic < Sedimentary Bed Indeterminate, major