Barstow_Formation

Barstow Formation

Barstow Formation

Geologic formation in the Mojave Desert near Barstow, San Bernardino County, California

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.[1][2]

Quick Facts Type, Lithology ...

It is of the early to middle Miocene epoch, (19.3 - 13.4 million years ago) in age, in the Neogene Period.[3] 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.[3] It is well known for its abundant vertebrate fossils including bones, teeth and footprints.[4] 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.[5]

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.[6]

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).[7][8][9]

See also

References

  1. [1]
    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.
  2. [2]
    Dibblee, T.W., Jr. (1968). Geology of the Fremont Peak and Opal Mountain Quadrangles, California. California Division of Mines and Geology, San Francisco.
  3. [3]
    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.
  4. [4]
    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.
  5. [5]
    Pagnac, Darrin C.; Reynolds, Robert E. (2006). "The fossil mammals of the Barstow Formation" (PDF). Making Tracks Across the Southwest: 65–70.
  6. [6]
    Palmer, A.R., Basset, A.M. (1954). Nonmarine Miocene arthropods from California. Science, Vol. 102, p.228-229
  7. [7]
    Lisa E. Park & Kevin F. Downing (2001). "Paleoecology of an exceptionally preserved arthropod fauna from lake deposits of the Miocene Barstow Formation, Southern California, U.S.A". PALAIOS. 16 (2): 175–184. Bibcode:2001Palai..16..175P. doi:10.1669/0883-1351(2001)016<0175:POAEPA>2.0.CO;2. S2CID 129795195.
  8. [8]
    Denton Belk & Frederick R. Schram (2001). "A new species of anostracan from the Miocene of California". Journal of Crustacean Biology. 21 (1): 49–55. doi:10.1651/0278-0372(2001)021[0049:ANSOAF]2.0.CO;2. JSTOR 1549760. S2CID 86407946.
  9. [9]
    D. Christopher Rogers & Jorge S. Coronel (2011). "A redescription of Branchinecta pollicifera Harding, 1940, and its placement in a new genus (Branchiopoda: Anostraca: Branchinectidae)". Journal of Crustacean Biology. 31 (4): 717–724. doi:10.1651/10-3449.1.
  • Syncline in the Barstow Formation exposed in Rainbow Basin near Barstow, California.
  • Syncline in the Barstow Formation, lower parking lot of Calico Ghost Town near Barstow, California.
  • Anticline in the Barstow Formation (Miocene) at Calico Ghost Town near Barstow, California.
  • Cameloid footprint (Lamaichnum alfi Sarjeant and Reynolds, 1999; convex hyporelief) from the Barstow Formation of Rainbow Basin, California.
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