Carbonate rocks of southeast Alaska

Unit symbol: Dlse
Age range Devonian (419.2 to 358.9 Ma)
Lithology: Sedimentary
Group name: Shallow-marine, carbonate-dominated rocks
Consists of thin-bedded to massive gray limestone of the Wadleigh and Black Cap Limestones; which locally contain minor shale and argillite interbeds, as well as the limestone members of the Cedar Cove and Karheen Formations, and the informal limestone of Kasaan Island. The Wadleigh Limestone on Prince of Wales Island is generally thick- to medium-bedded or massive limestone about 300 meters thick composed of fragmented shelly fossils in a dark, lime mudstone matrix and minor argillaceous and calcareous shale. Massive stromatoporoids may form reefs and reef breccia; brachiopods, gastropods, ostracodes, pelecypods, and crinoids make up substantial quantities of the coarse fossil detritus (Eberlein and others, 1983) and indicate an age range of Emsian (late Early Devonian) to Famennian (Late Devonian) (Eberlein and Churkin, 1970; Eberlein and others, 1983; Savage and Funai, 1980; Soja, 1988a). The significantly thicker Black Cap Limestone, in the Glacier Bay area (Rossman, 1963), is a structurally complex thin-bedded black limestone about 210 m thick that grades upward to a lighter colored, thicker-bedded to massive limestone about 1,160 m thick. Numerous fossils including rugose and tabulate corals, brachiopods, gastropods, ostracodes, stromatoporoids, and conodonts suggest an Early to Middle Devonian age for the unit (Blodgett and others, 2012). Limestone member of the Cedar Cove Formation is as thick as 350 m and consists of massive to thin-bedded fossiliferous limestone that contains interbeds of argillite and tuff and is locally metamorphosed to marble (Loney and others, 1963). Rugose and tabulate corals, stromatoporoids, brachiopods, mollusks, and trilobites provide a Middle Devonian to lower Upper Devonian (Frasnian) age for this unit (Loney and others, 1975). Additional collections indicate an age no younger than early Middle Devonian (Eifelian) for the limestone member of the Cedar Cove Formation (R.B. Blodgett, written commun., 2014). The limestone of Kasaan Island (Eberlein and others, 1983) is part of the Karheen Formation near Prince of Wales Island and similar limestone along Duncan Canal on Kupreanof Island are thin-bedded to massive fossiliferous limestone a couple hundred meters thick (Eberlein and others, 1983; Karl and others, 1999). As with the other limestone units in this map unit, this limestone is contains abundant fossil fragments of corals, stromatoporoids, brachiopods, conodonts, and crinoids, which here are of Emsian (late Early Devonian) to lower Eifelian (early Middle Devonian) age (Eberlein and others, 1983; Soja, 1988b; McClelland and Gehrels, 1990; Karl and others, 1999). Along Duncan Canal, the limestone also contains interbeds of argillite, sandstone, and volcanic rocks (Karl and others, 1999). Marble of the Gambier Bay Formation on Admiralty Island (Lathram and others, 1965), which may be age correlative, is included in map unit Dgbm here

Source map information

Source map Karl, S.M., Haeussler, P.J., and McCafferty, Anne, 1999, Reconnaissance geologic map of the Duncan Canal-Zarembo Island area, southeast Alaska: U.S. Geological Survey Open File Report 99-168, 1 sheet, scale 1:125,000. [http://pubs.usgs.gov/of/1999/of99-168/]
Symbol Dls
Unit name Fossiliferous limestone
Description Light to medium gray, medium-bedded to massive, fossiliferous limestone. Locally fetid. Contains subordinate interbedded argillite, sandstone, and volcanic rocks.
Lithology Sedimentary

Correlated geologic units

Label Dkfl
Description Kassan Limestone, part of Karheen
Geologic age Devonian to Middle-Devonian
Geologic setting Sedimentary, carbonate
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major