The Barstow Formation is a series of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s, conglomerates,

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s, siltstones and shales exposed in the

Mojave Desert The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily ...

near Barstow in

San Bernardino County San Bernardino County (), officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California, and is located within the Inland Empire area. As of the 2020 U.S. Census, the population was 2,181, ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

.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 The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

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 The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usu ...

North American land mammal age (

NALMA The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when re ...

). The sediments are fluvial and

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

in origin except for nine layers of

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

. It is well known for its abundant

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s including bones, teeth and

footprints Footprints are the impressions or images left behind by a person walking or running. Hoofprints and pawprints are those left by animals with hooves or paws rather than feet, while "shoeprints" is the specific term for prints made by shoes. The ...

.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

concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

s in its upper member, which contain three-dimensionally preserved

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

Fossils

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 A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...

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 Autochthon, autochthons or autochthonous may refer to: Fiction * Autochthon (Atlantis), a character in Plato's myth of Atlantis * Autochthons, characters in the novel ''The Divine Invasion'' by Philip K. Dick * Autochthon, a Primordial in the ...

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 Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered m ...

('' Archaebranchinecta barstowensis'').

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 Calico is a ghost town and former mining town in San Bernardino County, California, United States. Located in the Calico Mountains of the Mojave Desert region of Southern California, it was founded in 1881 as a silver mining town, and was later c ...

near Barstow, California. Image:BarstowFormationAnticlineMarch2010.jpg,

Anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

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,

. {{Neogene Footer Geologic formations of California Miocene California Lagerstätten Fossiliferous stratigraphic units of North America Paleontology in California Natural history of the Mojave Desert Geology of San Bernardino County, California

Fossils

Arthropods

See also

References