Sedimentary and volcanic rocks of the Orca Group, undivided

Unit symbol: Tovs
Age range Tertiary, Eocene to Paleocene (59.2 to 38 Ma)
Lithology: Sedimentary
Group name: Sedimentary and volcanic rocks of the Orca Group, undivided
Consists of locally variable amounts of tholeiitic basalt, and tuffaceous and generally minor turbiditic sedimentary rocks (Tysdal and Case, 1979; Nelson and others, 1985; Winkler and Plafker, 1993; Wilson and others, 2012) in Prince William Sound. Volcanic rocks are pillowed, and massive basalt flows, pillow breccia, and tuff are intermixed and interbedded with turbiditic mudstone, siltstone, and fossiliferous volcanogenic sandstone; locally nonvolcanogenic sandstone is interbedded (Winkler and Plafker, 1993). Locally subdivided into units Tos, below, and Togv, described with the volcanic rocks

Source map information

Source map Nelson, S.W., Dumoulin, J.A., and Miller, M.L., 1985, Geologic map of the Chugach National Forest: U.S. Geological Survey Miscellaneous Field Studies Map MF-1645B, scale 1:250,000 (Chugach NF Arc/Info coverage 1993).
Symbol Tosv
Unit name Orca Group -- Interbedded sedimentary and mafic volcanic rocks
Description Locally variable amounts of volcanic and sedimentary rocks. In some cases unit is marginal to thicker sequences composed of pillowed and massive basalt flows. The lithologies are quite variable throughout the study area. In Ragged mountains volcaniclastic and tuffaceous sedimentary rocks are abundant, and pillow basalt is rare. These rocks are typically metamorphosed to zeolite or prehnite-pumpellyite facies and on Knight Island they have been converted to a hard hornfels by the abundant sills(?). Interbedded sedimentary and mafic volcanic rocks
Lithology Sedimentary

Correlated geologic units

Label Tovs
Description Sedimentary and volcanic rocks of the Orca Group, undivided
Geologic age Late-Paleocene to Middle-Eocene
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Mafic-volcanic < Volcanic < Igneous Pyroclastic Indeterminate, major
Basalt < Mafic-volcanic < Volcanic < Igneous Flow Indeterminate, major
Greenstone < Metaigneous < Metamorphic Greenschist Indeterminate, major
Slate < Metaclastic < Metasedimentary < Metamorphic Greenschist Indeterminate, major
Sandstone < Clastic < Sedimentary Bed Indeterminate, major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major
Mudstone < Clastic < Sedimentary Bed Minor
Chert < Chemical < Sedimentary Bed Incidental