• Source: Siletz River Volcanics

The Siletz River Volcanics, located in the Oregon Coast Range, United States, are a sequence of basaltic pillow lavas that make up part of Siletzia. The basaltic pillow lavas originally came from submarine volcanoes that existed during the Eocene.




Description


The Paleocene to Eocene volcanics consist of volcanism flows and sills of tholeitic to alkalic basalts with associated tuff-breccia, siltstone and sandstone. The flows are vesiculated with zeolite filled amygdules.
The volcanics originated as oceanic crust and seamounts. Potassium argon dating gives ages of 58.1 ± 1.5 to 50.7 ± 3.1 Ma; Selandian to Ypresian.
The sequence has been divided into a lower pillowed tholeiitic unit and an upper porphyritic alkali basalt unit.
The volcanics occur in the following counties of western Oregon: Benton, Coos, Douglas, Lane, Lincoln, Polk, Tillamook, Washington and Yamhill.




= Fossil content

=
The sedimentary beds at the Ellendale Basalt and Portland Cement Company Quarries, interbeds in the upper part of the Siletz River volcanics, have provided fossils of the archaeogastropods Pleurotomaria (Entemnotrochus) baldwini, P. (E.) schencki and P. (E.) siletzensis.




See also






References






= Bibliography

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Hickman, C.S (1976), "Pleurotomaria (Archaeogastropoda) in the Eocene of the northeastern Pacific: a review of Cenozoic biogeography and ecology of the genus", Journal of Paleontology, 50: 1090–1102
Snavely, Parke D.; MacLeod, Norman S.; Wagner, Holly C. (1968), "Tholeiitic and alkalic basalts of the Eocene Siletz River Volcanics, Oregon Coast Range", American Journal of Science, 266 (6): 454–481, Bibcode:1968AmJS..266..454S, doi:10.2475/ajs.266.6.454




Further reading


Baldwin, E.M., 1974, Eocene stratigraphy of southwestern Oregon: Oregon Department of Geology and Mineral Industries Bulletin 83, 40 p.
Duncan, R.A., 1982, A captured island chain in the coast Range of Oregon and Washington: Journal of Geophysical Research, v. 87, p. 10, 827–10, 837
Snavely, P.D., MacLeod, N.S., and Wagner, H.C., 1973, Miocene tholeiitic basalts of coastal Oregon and Washington and their relations to coeval basalts of the Columbia Plateau: Geological Society of America Bulletin, v. 84, p. 387–424

Kata Kunci Pencarian:

• Siletz River Volcanics
• Siletz (disambiguation)
• Yellowstone hotspot
• List of fossiliferous stratigraphic units in Oregon
• Siletzia
• Willamette River
• Oregon Coast Range
• Mount Bailey (Oregon)
• Three Fingered Jack
• Rocky Butte