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Yamhill Formation and related rocks

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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
Geologic age Middle Eocene to Late Eocene
Lithologic constituents
Major
Sedimentary > Clastic > Siltstone (Bed)
Minor
Sedimentary > Clastic > Sandstone (Bed)
Incidental
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Pyroclastic-tuff)
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.
NGMDB product
Counties Clatsop - Coos - Douglas - Lincoln - Polk - Tillamook - Washington - Yamhill