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 Wilson, F.H., Mohadjer, Solmaz, Labay, K.A., and Shew, Nora, 2006, Digital datasets for geologic map by Wilson, F.H., Blodgett, R.B., Blome, C.D., Mohadjer, Solmaz, Preller, C.C., Klimasauskas, E.P., Gamble, B.M., and Coonrad, W.L.—Preliminary Integrated Geologic Map Databases for the United States: Digital Data for the Reconnaissance Bedrock Geologic Map for the Northern Alaska Peninsula area, Southwest Alaska: U.S. Geological Survey Open File Report 2006-1303, on-line only.
Symbol Jk
Unit name Graywacke of Kulukak Bay
Description A thick marine sedimentary unit referred to as "Weary graywacke" by Hoare and others, 1975. Mapped in the eastern part of the quadrangle by correlation with unit KJs of the adjacent Iliamna quadrangle. Typically consists of dark green or gray massive sandstone, although coarse pebble conglomerate is locally present. Locally hornfelsed. On final map, rocks in eastern part of quadrangle assigned to the Koksetna River sequence of Wallace and others (1989), NSA = 2855
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