Graywacke of Kulukak Bay of Hoare and Coonrad (1978)

Unit symbol: Jk
Age range Upper to Middle Jurassic (174.1 to 152.1 Ma)
Lithology: Sedimentary
Group name: Graywacke of Kulukak Bay of Hoare and Coonrad (1978)
Thick marine sedimentary unit that consists of very hard dark-green or gray, massive graywacke and siltstone and contains local coarse pebble conglomerate horizons. Compositionally, “varies from quartz- and plagioclase-rich wackes to quartz-poor volcanic wackes. Generally contains black argillite or tuff chips” (Hoare and Coonrad, 1978). Unit is a thick marine sedimentary unit earlier referred to as the “Weary graywacke” by Hoare and others (1975). Unit is widely exposed in the southern Goodnews Bay and Nushagak Bay quadrangles as well as the adjacent southeastern Dillingham quadrangle (Hoare and Coonrad, 1978). Buchia, Inoceramus, belemnites, and rare ammonite fragments that range in age from Middle to early Late Jurassic age have been found in this unit. Unit may be correlative with the Koksetna River sequence of Wallace and others, 1989, which is mapped as unit KJgn here. Locally subdivided by Box (1985) into a coherently and pervasively deformed volcaniclastic turbidite units

Source map information

Source map Hoare, J.M., and Coonrad, W.L., 1978, Geologic map of the Goodnews and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-B, 2 sheets, scale 1:250,000.
Symbol Jk
Unit name Graywacke of Kulukak Bay
Description A thick marine sedimentary unit referred to as "Weary graywacke" by Hoare and others, 1975. Consists of very hard graywacke and siltstone with local conglomerate.
Lithology Sedimentary

Correlated geologic units

Label Jkw
Description Graywacke of Kulukak Bay (Weary Graywacke)
Geologic age Middle-Jurassic to Kimmeridgian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Graywacke < Sandstone < Clastic < Sedimentary Bed Major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major
Conglomerate < Clastic < Sedimentary Bed Incidental
Black-shale < Shale < Mudstone < Clastic < Sedimentary Bed Incidental