Barstow Formation
{{Short description|Geologic formation in the Mojave Desert near Barstow, San Bernardino County, California}}
{{Infobox rockunit
| name = Barstow Formation
| image = BarstowFormationMarch2010.jpg
| caption = Barstow Formation exposed in Owl Canyon near Barstow, California.
| type = Sedimentary
| period = Miocene
| age = Early to Middle Miocene (Barstovian)
~{{Fossil range|19.3|13.4}}
| prilithology = limestone, shale, siltstone, sandstone, tuff
| otherlithology = conglomerate
| namedfor = Barstow, California
| namedby = Hershey (1902)
| region = Mojave Desert,
California
| country = United States
| coordinates =
| unitof =
| subunits =
| underlies =
| overlies =
| thickness =
| extent = Northern San Bernardino County, Southeastern California
| area =
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| map_caption =
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The Barstow Formation is a series of limestones, conglomerates, sandstones, siltstones and shales exposed in the Mojave Desert near Barstow in San Bernardino County, California.Dibblee, T.W., Jr. (1967). Areal Geology of the Western Mojave Desert, California. Geological Survey Professional Paper no. 522. United States Government Printing Office, Washington D.C.Dibblee, T.W., Jr. (1968). Geology of the Fremont Peak and Opal Mountain Quadrangles, California. California Division of Mines and Geology, San Francisco.
It is of the early to middle Miocene epoch, (19.3 - 13.4 million years ago) in age, in the Neogene Period.Woodburne, M.O., Tedford, R.H., Swisher III, C.C. (1990). Lithostratigraphy, biostratigraphy, and geochronology of the Barstow Formation, Mojave Desert, southern California: Geological Society of America Bulletin, Vol. 102, p. 459-477. It lends its name to the Barstovian North American land mammal age (NALMA).
The sediments are fluvial and lacustrine in origin except for nine layers of rhyolitic tuff. It is well known for its abundant vertebrate fossils including bones, teeth and footprints.Lindsay, E.H. (1972). Small Mammal Fossils from the Barstow Formation, California. University of California Publications in Geological Sciences, Vol. 93. University of California Press, Berkeley. The formation is also renowned for the fossiliferous concretions in its upper member, which contain three-dimensionally preserved arthropods.
Fossils
= Mammals =
Mammals from various groups are found in the Barstow Formation. Herbivorous groups include horses, peccaries, oreodonts, camels, proghorns and other horned artiodactyls, proboscideans, and a rhinoceros. The unit also produces a surprising number of carnivorous mammals, reminiscent of the modern east African savanna to which it has been compared climatically and ecologically. These include a number of borophagines, mustelids, nimravids, Amphicyon, and the primitive bear Hemicyon.{{Cite journal |last=Pagnac |first=Darrin C. |last2=Reynolds |first2=Robert E. |date=2006 |title=The fossil mammals of the Barstow Formation |url=https://www.desertsymposium.org/publications/2006_making_tracks.pdf |journal=Making Tracks Across the Southwest |pages=65-70}}
= Arthropods =
The arthropods in the upper member of the Barstow Formation are preserved in concretions. The concretions are calcareous and range from 0.125 cm3 to 125 cm3. The fossils are typically three-dimensional and, on occasion, exhibit internal anatomy. Due to the preservation of soft-tissue, the Barstow Formation has been identified as a Konservat-Lagerstätte deposit. The fauna was first recognized in 1954 by Allen M. Basset and Allison "Pete" R. Palmer.Palmer, A.R., Basset, A.M. (1954). Nonmarine Miocene arthropods from California. Science, Vol. 102, p.228-229
The concretions from the Barstow Formation preserve both allochthonous arthropod communities and rare autochthonous arthropod communities. Over 21 orders of arthropods have been recorded. The fossil assemblage is dominated by Diptera (Dasyhelea australis antiqua), Coleoptera (Schistomerus californese), and Anostraca (Archaebranchinecta barstowensis).{{Cite journal |author=Lisa E. Park & Kevin F. Downing |year=2001 |title=Paleoecology of an exceptionally preserved arthropod fauna from lake deposits of the Miocene Barstow Formation, Southern California, U.S.A |journal=PALAIOS |volume=16 |issue=2 |pages=175–184 |doi=10.1669/0883-1351(2001)016<0175:POAEPA>2.0.CO;2|bibcode=2001Palai..16..175P |s2cid=129795195 }}{{cite journal |author=Denton Belk & Frederick R. Schram |year=2001 |title=A new species of anostracan from the Miocene of California |journal=Journal of Crustacean Biology |volume=21 |issue=1 |pages=49–55 |doi=10.1651/0278-0372(2001)021[0049:ANSOAF]2.0.CO;2 |jstor=1549760|s2cid=86407946 }}{{cite journal |author=D. Christopher Rogers & Jorge S. Coronel |year=2011 |title=A redescription of Branchinecta pollicifera Harding, 1940, and its placement in a new genus (Branchiopoda: Anostraca: Branchinectidae) |journal=Journal of Crustacean Biology |volume=31 |issue=4 |pages=717–724 |doi=10.1651/10-3449.1|doi-access=free }}
See also
References
Image:Rainbow Basin.JPG|Syncline in the Barstow Formation exposed in Rainbow Basin near Barstow, California.
Image:SynclineCalico.JPG|Syncline in the Barstow Formation, lower parking lot of Calico Ghost Town near Barstow, California.
Image:BarstowFormationAnticlineMarch2010.jpg|Anticline in the Barstow Formation (Miocene) at Calico Ghost Town near Barstow, California.
Image:CamelFootprintBarstowMiocene.jpg|Cameloid footprint (Lamaichnum alfi Sarjeant and Reynolds, 1999; convex hyporelief) from the Barstow Formation of Rainbow Basin, California.
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Category:Geologic formations of California
Category:Fossiliferous stratigraphic units of North America
Category:Paleontology in California
Category:Natural history of the Mojave Desert
Category:Geology of San Bernardino County, California
Category:Limestone formations of the United States
Category:Shale formations of the United States
Category:Siltstone formations of the United States
Category:Sandstone formations of the United States