Kootznahoo Formation

Unit symbol: Tk
Age range Tertiary, lower Miocene to upper Eocene (66 to 15.97 Ma)
Lithology: Sedimentary
Group name: Kootznahoo Formation
Light-greenish-gray, nonmarine, lithofeldspathic sandstone, siltstone, mudstone, and conglomerate that contains coal fragments and lenses in the Zarembo and Kuiu Islands region (Brew and others, 1984) and on Admiralty Island (Lathram and others, 1965) of southeast Alaska. Polymictic conglomerate contains sandstone, argillite, coal, phyllite, limestone, chert, schist, gneiss, granitic rocks, volcanic rocks, and quartz. Includes lignite and subbituminous coal beds up to 1.5 m thick. Outcrop area is wedge-shaped at Kootznahoo Inlet near Angoon, apparently filling an asymmetric graben, and unit is up to 2,000 m thick at south margin of graben. Plant collections from Port Camden on Kuiu Island, on Kupreanof Island, and at Little Pybus Bay on Admiralty Island were assigned an Eocene age by Knowlton in Buddington and Chapin (1929), but were reevaluated as Paleocene by Jack Wolfe in Lathram and others (1965). Plant fossils in Kootznahoo Inlet on Admiralty Island include “Ulmus” pseudobrauni, Octea sp., Dilleniaceae, and Dryophyllum sp., of late Eocene to earliest Oligocene age (Lathram and others, 1965), Carya magnifica, Juglans orientalis, Alnus alaskana, Cercidyphyllum aff. C. crenatum, Vitis atwoodi, Populus sp., and Ficus alaskana of Oligocene age, and Fagus antipofi, Quercus furujelmi, Comptonia naumani, and Populus lindgreni of early Miocene age (Lathram and others, 1965). Age reported to be Paleocene and Eocene in the Zarembo-Kuiu Islands region and Eocene to Miocene on Admiralty Island (Brew and others, 1984)

Source map information

Source map Karl, S.M., 2013, Unpublished data.
Symbol Tk
Unit name Kootznahoo Formation
Description Fluvial nonmarine arkosic sandstone, sandstone, shale, and conglomerate; medium- to very thick-bedded; locally cross-bedded; dominant rock type is medium- to very coarse-grained lithic feldspathic quartz arenite. Light greenish gray, nonmarine lithofeldspathic sandstone, siltstone, mudstone, and conglomerate, with coal fragments and lenses. Polymictic conglomerate contains sandstone, argillite, coal, phyllite, limestone, chert, schist, gneiss, granitic rocks, volcanic rocks, and quartz. Unit includes lignite and subbituminous coal beds up to 1.5 m thick. Unit is wedge-shaped at Kootznahoo Inlet, apparently filling an asymmetric graben, up to 2000 m thick at the south margin. Unit underlies Oligocene volcanic rocks at Little Pybus Bay on Admiralty Island. A significant section is exposed in Hamilton, Dakaneek, and Big John Bays on Kupreanof Island, and in the Port Camden area of Kuiu Island. Nonmarine siltstone, sandstone, and conglomerate with scattered lignite layers and abundant carbonaceous fragments. At Coal Bay, Prince of Wales Island, light gray to buff, gently dipping graywacke sandstone containing carbonized logs with branches still attached. At Little Coal Bay, sandstone is accompanied by conglomerate with rounded cobbles of quartz diorite and argillite to 25 cm in diameter; sandstone includes seams of marcasite-bearing lignitic coal up to 10 cm thick
Lithology Sedimentary

Correlated geologic units

Label Tkz
Description Kootznahoo Formation, light greenish gray, medium- to coarse-grained, friable, lithofeldspathic fluvial sandstone and siltstone containing leaf fragments and rare, cm-scale, coal lenses
Geologic age Paleocene to Early-Miocene
Geologic setting Sedimentary, continental
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Indeterminate, major
Arkose < Sandstone < Clastic < Sedimentary Bed Indeterminate, major
Siltstone < Clastic < Sedimentary Carbonaceous Indeterminate, major
Shale < Mudstone < Clastic < Sedimentary Bed Incidental