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Hood Bay Formation

Unit symbol: DOhb
Age range Lower? Devonian to Ordovician (485.4 to 393.3 Ma)
Lithology: Sedimentary
Group name: Shale, chert, and argillite
Black argillite, thin-bedded black chert, thin-bedded black limestone, brown calcareous and carbonaceous wacke sandstone, graywacke, and dull green pillow basalt. The chert, argillite, and limestone contain radiolarians. Graywacke clasts include mainly chert, with subordinate limestone, sandstone, argillite, and volcanic rock fragments. Pillow basalts have interbeds of argillite and gray green tuffaceous siltstone. Karl and others (2010, p. 2) indicated that deformed, quartz-veined black chert and argillite containing Ordovician graptolites (Carter, 1977) grade upward to carbonaceous argillite, chert, chert sandstone grit, meter-scale lenses of pillow basalt, and thinly laminated black limestone containing Silurian-Devonian conodonts (A.G. Harris, written commun., 1995). Crisscrossing quartz veinlets in the Hood Bay Formation, which are absent in the Cannery Formation (unit PDcf), are inferred to represent a pre-Cannery deformation event

Source map information

Source map Karl, S.M., Haeussler, P.J., Himmelberg, G.R., and Brew, D.A., 1998, Unpublished data.
Symbol DOh
Unit name Hood Bay Formation
Description Black argillite, thin-bedded black chert, thin-bedded black limestone, brown calcareous and carbonaceous wacke sandstone, graywacke, and dull green pillow basalt. The chert, argillite, and limestone contain radiolarians. Graywacke clasts include mainly chert, with subordinate limestone, sandstone, argillite, and volcanic rock fragments. Pillow basalts have interbeds of argillite and gray green tuffaceous siltstone.
Lithology Sedimentary

Correlated geologic units

Label Ohb
Description Hood Bay Formation, black argillite, black chert, and black limestone (SI008, SI100)
Geologic age Ordovician to Early-Devonian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Argillite < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major
Limestone < Carbonate < Sedimentary Calcareous Indeterminate, major
Chert < Chemical < Sedimentary Bed Indeterminate, major