Cannery Formation and Porcupine slate of Redman and others (1985), undivided

Unit symbol: PDcf
Age range Permian to Devonian (419.2 to 272.3 Ma)
Lithology: Sedimentary
Group name: Cannery Formation and Porcupine slate of Redman and others (1985), undivided
Cherty graywacke and argillite that contains subordinate conglomerate, limestone, and volcanic rock interbeds; locally metamorphosed to slate, phyllite, marble, greenstone, and hornfels; intensely folded (Loney, 1964; Lathram and others, 1965; Muffler, 1967; Brew and others, 1984; Redman and others, 1985; Karl and others, 2010). Includes the Porcupine slate of Redman and others (1985) and undifferentiated chert, marble, and argillite mapped by Gilbert (1988). Graywacke, tuff, and chert are commonly interbedded, deposited as turbidites. Graywacke beds are up to 5 m thick and dominantly consist of volcanic and calcareous rock fragments. Limestone occurs in beds up to 50 cm thick, and pillow basalt and tuff-breccia horizons are as thick as 100 m. Total thickness of the Cannery Formation is estimated to be greater than 500 m (Karl and others, 2010). Limestone of the Cannery Formation contains Permian bryozoans and crinoids on Admiralty Island (Lathram and others, 1965). Chert contains Mississippian to Permian radiolarians (Karl and others, 2010). On Kupreanof Island, chert and limestone contain Early Pennsylvanian to early Permian radiolarians, early Permian conodonts, and Upper Mississippian conodonts (Karl and others, 1999). Here, also includes calcareous schist and semischist on northwestern Admiralty Island that were previously mapped as part of the Retreat Group by Lathram and others (1965). The Cannery Formation is likely correlative with the Porcupine slate of Redman and others (1985) (unit |ps). Also included here is a unit of siliceous phyllite and metachert on Admiralty Island of similar age to rocks at the base of the defined Cannery Formation (Karl and others, 2010) of Late Devonian age. Co-author S.M. Karl considers these siliceous phyllites and metacherts to be a separate unit, but we include them here

Source map information

Source map Karl, S.M., Haeussler, P.J., Himmelberg, G.R., and Brew, D.A., 2002, Unpublished data.
Symbol Dsc
Unit name Siliceous phyllite and metachert of Hawk Inlet
Description Dark gray to black siliceous phyllite, black siliceous slate, phyllite, quartzite, and metachert that contain thin, cm- to m-scale lenses of metalimestone were previously assigned to the Retreat Group by Lathram and others (1965), later assigned to map unit Mzps by Brew and Ford (1985), and are herein distinguished as a new unit. Siliceous phyllite, quartzite, and metachert alternate on a meter scale. Quartz-rich metaclastic rocks have rhythmic bedding and include graded beds, suggestive of deposition as turbidites. The northeast boundary of the unit is faulted against sooty black argillite similar to the rocks assigned to the Cannery Formation on the west flank of Eagle Peak that contain the Early Permian brachiopod Muirwoodia. The slate and quartzite include an increasing proportion of metavolcaniclastic rocks from north to south in Hawk Inlet. The siliceous phyllite and metachert are metamorphosed, folded, and deformed, with folded segregation layering that records three deformation events, and stratigraphic relations to adjacent units are not clear. Metamorphic mineral assemblages for quartzite include quartz-albite-chlorite-calcite-white mica-graphite-pyrite. The mineral assemblage for siliceous phyllite includes quartz-albite-chlorite-white mica-graphite and quartz-albite-chlorite-calcite-white mica-graphite. The mineral assemblage for volcaniclastic semischist includes quartz-albite-chlorite-calcite-white mica-graphite. The mineral assemblage for greenstone includes albite-chlorite-epidote-calcite-white mica-titanite. These mineral assemblages are compatible with greenschist facies metamorphism. Conodonts have a CAI of 5-5.5 (A. Harris, written communication, 2000) which indicates temperatures consistent with greenschist facies conditions (Rejebian, V.A., Harris, A.G., and Huebner, J.S., 1987). The metachert of Hawk Inlet is similar in age to chert of the Cannery Formation on Kupreanof Island, but it is not included in the Cannery Formation because it is significantly more deformed and recrystallized than adjacent rocks of the Cannery Formation in the area of Hawk Inlet. The metamorphic mineral assemblages of the metachert of Hawk Inlet are similar to those of Pzcs and Pzgs, which suggests a similar metamorphic history and potential stratigraphic relationship for these 3 units. The siliceous phyllite and metachert of Hawk Inlet have a younger age than the rocks at Point Retreat and lack the upper greenschist facies metamorphic minerals commonly found in the rocks at Point Retreat
Lithology Metamorphic

Correlated geologic units

Label Du
Description Southeast Alaska undivided Devonian rocks
Geologic age Devonian
Geologic setting Undivided
Lithology Form Importance
Marble < Metacarbonate < Metasedimentary < Metamorphic Greenschist Major
Metagraywacke < Metasandstone < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Pelitic-schist < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major