Siletz River Volcanics
{{short description|Sequence of basaltic pillow lavas that make up part of Siletzia}}
{{Infobox rockunit
| name = Siletz River Volcanics
| image = OregonCoastRangeRocks.JPG
| caption = Exposed pillow lava in the Northern range
| type = Formation
| age = Selandian-Ypresian (Tiffanian-Bridgerian)
{{fossil range|59.6|47.6}}
| period = Thanetian
| prilithology = Sills of tholeitic to alkalic basalts
| otherlithology = Tuff breccia, siltstone, sandstone
| namedfor = Siletz River
| namedby =
| year_ts =
| region = Benton, Coos, Douglas, Lane, Lincoln, Polk, Tillamook, Washington & Yamhill Counties, Oregon
| country = {{USA}}
| coordinates = {{coord|44.9|N|123.4|W|display=inline,title}}
| paleocoordinates = {{coord|47.0|N|107.5|W|display=inline}}
| unitof =
| subunits =
| underlies = Yamhill Formation
| overlies =
| thickness =
| extent =
| area =
| map = {{Location map+ | United States#Oregon
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | United States#Oregon
| lat_deg = 44.9
| lon_deg = -123.4
| mark = Orange ff8040 pog.svg
| marksize = 12
}}
}}
| map_caption =
}}
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.[https://paleobiodb.org/classic/displayStrata?geological_group=&formation=Siletz%20River%20Volcanics%20&group_formation_member=Siletz%20River%20Volcanics%20 Siletz River Volcanics] at Fossilworks.org{{cite web |url=https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=ORTsr%3B0 |title=Siletz River Volcanics and related rocks |work=USGS Mineral Resources On-Line Spatial Data |publisher=U.S. Geological Survey }} 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.Snavely et al., 1968
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.Hickman, 1976
See also
{{div col}}
- Coldwater Beds of British Columbia
- Golden Valley Formation of North Dakota
- Hanna Formation of Wyoming
- Indian Meadows Formation of Wyoming
- Margaret Formation of Ellesmere Island, Northwest Territories and Nunavut
- Nanjemoy Formation of Virginia, Maryland and District of Columbia
- Paskapoo Formation of Alberta
- Wasatch Formation of Colorado, Idaho, Montana, New Mexico, Wyoming and Utah
- Washakie Formation of Colorado and Wyoming
- Willwood Formation of Wyoming
{{div col end}}
References
{{Reflist|3}}
= Bibliography =
- {{citation |last=Hickman |first=C.S |year=1976 |title=Pleurotomaria (Archaeogastropoda) in the Eocene of the northeastern Pacific: a review of Cenozoic biogeography and ecology of the genus |journal=Journal of Paleontology |volume=50 |pages=1090–1102}}
- {{citation |first1=Parke D. |last1=Snavely |first2=Norman S. |last2=MacLeod |first3=Holly C. |last3=Wagner |year=1968 |title=Tholeiitic and alkalic basalts of the Eocene Siletz River Volcanics, Oregon Coast Range |url=http://www.ajsonline.org/cgi/content/abstract/266/6/454 |journal=American Journal of Science |volume=266 |issue=6 |pages=454–481 |doi=10.2475/ajs.266.6.454|bibcode=1968AmJS..266..454S }}
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
Category:Paleogene geology of Oregon
Category:Paleocene Series of North America
Category:Eocene Series of North America
Category:Seamounts of the Pacific Ocean
Category:Sandstone formations of the United States