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Yamhill Formation and related rocks (upper and middle Eocene)

Massive to thin-bedded concretionary marine siltstone and thin interbeds of arkosic, glauconitic, and basaltic sandstone; locally contains interlayered basalt lava flows and lapilli tuff. Foraminiferal assemblages in siltstone referred to the Ulatisian and lower Narizian Stages (Snavely and others, 1969; McKeel, 1980) Includes the Elkton Formation of Baldwin (1974; also see Beaulieu and Hughes, 1975), which consists of thin-bedded siltstone and minor sandstone interbeds
State Oregon
Name Yamhill Formation and related rocks (upper and middle Eocene)
Geologic age Middle Eocene to Late Eocene
Primary rock type siltstone
Secondary rock type sandstone
Other rock types basalt; tuff
Lithologic constituents
Major
Sedimentary > Clastic > Siltstone (Bed)
Minor
Sedimentary > Clastic > Sandstone (Bed)
Incidental
Igneous > Volcanic > Mafic-volcanic > Basalt (Bed)
Igneous > Volcanic > Mafic-volcanic > Basalt (Pyroclastic, tuff)
Map references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Unit references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Snavely, P.D., Jr., McLeod, N.S., and Rau, w.w., 1969, Geology of the Newport area, Oregon: The Ore Bin, v. 31, p. 25-71.
McKeel, D.R., 1980, Micropaleontological study of five wells, western Willamette Valley, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report 0-80-1, 21 p.
Baldwin, E.M., 1974, Eocene stratigraphy of southwestern Oregon: Oregon Department of Geology and Mineral Industries Bulletin 83, 40 p.
Beaulieu, J.D., and Hughes, P.W., 1975, Environmental geology of western Coos and Douglas Counties, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 87, 148 p.
Counties Clatsop - Douglas - Lincoln - Polk - Tillamook - Washington - Yamhill