File:Volcanic breccia (Sonoma Volcanics, Upper Pliocene, 3.2-3.4 Ma; Calistoga Petrified Forest, Calistoga, California, USA) 5 (49092952967).jpg
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| Description |
Volcanic breccia in the Pliocene of California, USA. Volcanic breccia is a clastic-textured, poorly-sorted, extrusive igneous rock. It has a mix of large and small grains, with the large grains being angular in shape. This rock forms by deposition, burial, and lithification of material expelled during explosive volcanic eruptions. The larger grains in this sample aren't very sizable, but I am still inclined to call this a volcanic breccia. I don't know what the cutoff point is between a volcanic tuff (= all ash) and volcanic breccia (= lots of large angular grains). The outcrop seen here is at California's Calistoga Petrified Forest, which has been called the best-anywhere fossil forest of Pliocene age. Fossil wood at this site is preserved with the most common permineralization mineral - quartz. The preservation of these trees was the result of burial by a rhyolitic pyroclastic flow deposit of the Sonoma Volcanics (Upper Pliocene). The ash and rock fragments were erupted from a vent near modern-day Mt. St. Helena (= north of this locality). Stratigraphy: Sonoma Volcanics, Upper Pliocene, 3.2 to 3.4 Ma Locality: Calistoga Petrified Forest, northern side of Petrified Forest Road, west-southwest of the town Calistoga, eastern Sonoma County, Coast Ranges of northwest-central California, USA |
| Date | |
| Source | Volcanic breccia (Sonoma Volcanics, Upper Pliocene, 3.2-3.4 Ma; Calistoga Petrified Forest, Calistoga, California, USA) 5 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/49092952967 (archive). It was reviewed on 23 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 02:43, 23 November 2019 | | 3,008 × 2,000 (4.69 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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