Karheen and Cedar Cove Formations

Unit symbol: Dcc
Age range Devonian (419.2 to 372.2 Ma)
Lithology: Sedimentary
Group name: Karheen and Cedar Cove Formations
Karheen Formation has two facies: an upper shallow-water sandstone, shale and conglomerate facies, and a lower deep-water facies. According to R.B. Blodgett (written commun., 2014), the Karheen Formation, as used here, is much more complex than generally described. Much of it is Silurian in age and there is another unnamed unit likely included here. The shallow-water facies, about 1,800 m thick, contains minor well-bedded and penecontemporaneously deformed platy limestone in addition to its clastic components and is characterized by red beds, calcareous cement, festoon crossbedding, ripple marks, and mud cracks. Clasts are mainly volcanic rocks and chert, but pebbles to boulders of sedimentary rocks and felsic to mafic plutonic rocks are also present (Eberlein and others, 1983). Locally the limestone contains abundant brachiopods. Unconformably overlies Staney Creek unit of Eberlein and others (1983) and the Descon Formation. Eberlein and others (1983) reported that abundant detrital K-feldspar and bronze-colored biotite in the sandstone distinguishes the Karheen from older sandstone, but S.M. Karl (unpub. data, 2013) noted that, upon thin-section examination, detrital K-feldspar is not abundant in this facies. The deep water facies consists of matrix-supported debris-flow deposits, which were described by Gehrels (1992) as a sedimentary breccia composed of unsorted clasts of plutonic rocks and highly deformed volcanic, sedimentary and intrusive rocks that are as large as 50 cm in diameter. The clasts are moderately flattened, tectonically brecciated, and locally semischistose (Gehrels, 1992). Eberlein and Churkin (1970) described the deep-water facies as green-gray, gray, and reddish-brown lithic wacke and graywacke and minor siltstone; red, red-brown, and green shale; thin-bedded sandy limestone; contorted platy limestone; pebble-to-cobble polymictic conglomerate; and biostromal limestone and reef breccia. Sandstone and shale is commonly graded and contains festoon cross bedding, ripple marks, and mud cracks (Eberlein and Churkin, 1970). Latest Lower Devonian or earliest Middle Devonian (Pragian or younger) graptolites Monograptus pacificus are reported (Churkin and others, 1970). Eberlein and others (1983) also describe “graptolite and plant-bearing shale interbedded with graywacke, sandstone, and conglomerate.” The vascular plants preserved in this unit are the oldest plant fossils known in North America (Churkin and others, 1969). Eberlein and others (1983) also report subordinate andesitic volcanic rocks and that “the youngest beds of the sequence appear to be a 200 m thick section of interbedded andesitic flows, broken pillow breccia, and tuff.” These volcanic rocks are included in unit Dmv here. The Cedar Cove Formation, on Chichagof Island, consists of up to 900 m of thin-bedded argillite and minor limestone, turbiditic graywacke, and conglomerate. Conglomerate clasts include “volcanic rock, granite, alaskite, syenite, graywacke, quartz, chert, and limestone” (Loney and others, 1975, p. 10). Graywacke contains large pink K-feldspar, plagioclase, quartz, pyrite grains, and volcanic rock fragments (Loney and others, 1975; Karl and others, 1999). Locally, includes the limestone member of the Cedar Cove Formation (unit Dlse). Loney and others (1975) reported Middle Devonian to Frasnian (lower Upper Devonian) corals, stromatoporoids, brachiopods, and a trilobite. Karl (1999) reported Emsian (upper Lower Devonian) conodonts from the lower member of the Cedar Cove Formation

Source map information

Source map Karl, S.M., 2013, Unpublished data.
Symbol Drl
Unit name Sandstone and conglomerate
Description On Chichagof Island, unit includes Cedar Cove Formation; lower member is a mixed argillite, tuff, limestone, and graywacke; upper member is dominantly limestone. Gradationally overlies Kennel Creek limestone, base is marked by first graywacke bed. Graywacke contains quartz, plagioclase, potassium feldspar, biogenic debris, limestone, volcanic rock fragments, and secondary pyrite, chlorite, and epidote. Graywacke forms turbidites, debris flows, and crossbeds, and is locally conglomeratic. Conglomerate contains pebbles and cobbles of granite, syenite, limestone, graywacke, chert, quartz and limestone. The upper member consists of medium to thick-bedded gray, fetid, fossiliferous limestone, and black, organic calcareous mudstone. Red arkose and red polymictic conglomerate in Saginaw Bay overlie Kuiu Limestone, and contains quartz, plagioclase, and chert but no K-feldspar or detrital mica have been reported. On Prince of Wales Island unit includes Karheen Formation, composed of sandstone, shale, and pebble, cobble, and boulder conglomerate characterized by redbeds, calcareous cement, and crossbedding (commonly of festoon type). Locally contains thin- to medium-bedded gray limestone, calcareous pyritic siltstone, and thin-bedded platy limestone. Sandstone is green, green-gray, and reddish-brown lithic wacke and graywacke. Shale is silty and red or green. Conglomerate clasts vary in lithology: mainly mafic volcanic clasts and greenish-gray chert, but graywacke, siltstone, red chert, quartzite, white quartz, and limestone are present. Granitoid clasts are generally rare. To the north the Karheen is mainly sandstone and shale that lie conformably on Heceta Limestone. In the south, Karheen is dominantly conglomerate and rests unconformably on Descon Formation. Thickness about 6000 feet. red sandstone, shale, and conglomerate, with subordinate platey thin-laminated limestone. Unit is characterized by redbeds with festoon crossbeds, ripple marks, and mudcracks. Conglomerate clasts include mainly volcanic rocks and chert, with subordinate arkose, graywacke, siltstone, quartz, limestone, and felsic to mafic intrusive rocks. Detrital K-feldspar and biotite distinguish Karheen sandstone from older sandstones. Mudstone locally contains ostracods, and contains Early Devonian plant fossils. Limestone is penecontemporaneously deformed. Unit conformably overlies Heceta limestone and gradationally overlies Staney Creek redbeds and limestone. Unit is laterally gradational to, and underlies Wadleigh limestone. Unit is locally as thick as 1800 m. In Hessa Inlet area, includes tan to reddish-brown-weathering sandstone, siltstone, and subordinate mudstone and pebbly conglomerate, interbedded locally with fossiliferous limestone and maroon and green shale. At Hessa Inlet-Bert Millar Cutoff area, unit includes tan- to reddish-brown-weathering pebble, cobble, and boulder conglomerate, pebbly sandstone, and subordinate sandstone, siltstone, and volcanic rocks. Massive to thick-bedded with channels and high angle crossbeds. Subaerial to shallow marine. Unit also includes plagioclase porphyritic volcanic rocks. Sandstone ranges from massive beds several meters in thickness to thin beds with high angle crossbeds and channels. Sandstone contains monocrystalline quartz and feldspar, and granitic and felsic to mafic volcanic lithic fragments. Unit gradationally overlies conglomerate. Shallow marine, stratigraphic thickness exceeds 1 km
Lithology Sedimentary

Correlated geologic units

Label Drl
Description Cedar Cove Formation
Geologic age Early-Devonian to Frasnian
Geologic setting Undivided
Lithology Form Importance
Limestone < Carbonate < Sedimentary Bed Major
Graywacke < Sandstone < Clastic < Sedimentary Bed Major
Limestone < Volcanic < Igneous Pyroclastic, tuff Indeterminate, major
Argillite < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major