Older volcanic rocks of southwest Alaska

Unit symbol: Trvsw
Age range Triassic (235 to 208.5 Ma)
Lithology: Igneous - Volcanic
Group name: Massive basalt and greenstone
Massive pillow basalt and basaltic breccia interbedded with thin-bedded tuffaceous chert and shale in the Bethel quadrangle (Box and others, 1993) and inferred to extend into the Taylor Mountains quadrangle. Also included here are volcanic rocks as thick as 60 m interbedded with cherty siltstone in the northwestern Taylor Mountains quadrangle (Sainsbury and MacKevett, 1965) between splays of the Holitna Fault. These volcanic rocks are associated with sparsely distributed limestone that yields Monotis and Halobia fossils of Late Triassic (Norian) age (Miller and others, 2007)

Source map information

Source map Box, S.E., Moll-Stalcup, E.J., Frost, T.P., and Murphy, J.M., 1993, Preliminary geologic map of the Bethel and southern Russian Mission quadrangles, southwestern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2226-A, 1 sheet, scale 1:250,000.
Symbol Trb
Unit name Togiak Terrane; Pillow basalt and minor interbedded chert
Description Massive pillow basalt and basaltic breccia interbedded with thin-bedded tuffaceous chert and shale
Lithology Igneous

Correlated geologic units

Label Trmb
Description Mafic volcanic rocks of southwest Alaska
Geologic age Late-Triassic to Norian
Geologic setting Extrusive, mafic
Lithology Form Importance
Basalt < Mafic-volcanic < Volcanic < Igneous Flow, pillows Major
Basalt < Mafic-volcanic < Volcanic < Igneous Volcaniclastic, volcanic breccia Indeterminate, major