Unit symbol: | Tovs |
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Age range | Tertiary, Eocene to Paleocene (59.2 to 38 Ma) |
Lithology: | Sedimentary |
Group name: | Sedimentary and volcanic rocks of the Orca Group, undivided |
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, pamphlet, 16 p., 1 sheet, scale 1:250,000 (Chugach NF Arc/Info coverage 1993). |
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Symbol | Tops |
Unit name | Orca Group -- Pillow basalt and sedimentary rocks |
Description | Pillow basalt, massive basalt flows, minor volcanic breccia interbedded with sandstone, siltstone, and shale. Distinguished from the interbedded sedimentary and mafic volcanic rocks unit on the basis of the predominance of pillow basalt in the section. Probably gradational with the pillow basalt unit. Two measured sections on Ellamar Mountain show significant differences in the percent of interbedded volcanic and sedimentary rocks that reflect rapid lensing out of units probably due to the presence of an irregular paleosurface. One section contains 92 percent volcanic rocks and 8 percent sedimentary rocks, and the other section about 1,200 ft laterally distant contains 75 percent volcanic rocks and 25 percent sedimentary rocks. |
Lithology | Igneous |
Label | Tovs |
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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 |
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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 |