Barstovian

Barstovian
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Name	Barstovian
Period	Miocene
Time start	16.3
Time end	13.6
Chronology	North American Land Mammal Ages

Barstovian The Barstovian is a North American Land Mammal Age (NALMA) used to subdivide the Middle Miocene interval, widely employed in paleontology, stratigraphy, and paleoecology. It serves as a temporal framework for correlating fossil localities across basins such as the Great Plains, Central Valley (California), and Pacific Northwest and for comparing assemblages to Eurasian stages like the Serravallian and Langhian. Researchers from institutions such as the Smithsonian Institution, University of California, Berkeley, and American Museum of Natural History have applied the Barstovian in studies involving formations like the Barstow Formation, John Day Formation, and Ogallala Formation.

Definition and temporal range

The Barstovian was originally defined on the basis of mammalian faunal horizons and is commonly placed between roughly 16.3 and 13.6 million years ago, overlapping the Langhian and early Serravallian stages of the Miocene. Key temporal markers include first and last appearances of taxa used in correlations with European stages represented in works by researchers at Stanford University, University of Michigan, and Yale University. Regional chronologies often tie Barstovian boundaries to magnetostratigraphic chrons established by teams from Lamont–Doherty Earth Observatory and US Geological Survey.

Geologic context and stratigraphy

Barstovian deposits occur in diverse stratigraphic contexts, including fluvial, lacustrine, and volcaniclastic sequences such as the Barstow Formation, Ogallala Formation, John Day Formation, Harrison Formation, and Rattlesnake Formation. These units have been correlated using biostratigraphy, magnetostratigraphy, and radiometric dates from volcanic ash beds studied at laboratories like Lawrence Berkeley National Laboratory and Los Alamos National Laboratory. Stratigraphers reference regional frameworks such as the Colorado Plateau, Great Basin, and Gulf Coastal Plain to map Barstovian exposures, integrating work by geologists affiliated with USGS, California Geological Survey, and the British Geological Survey.

Paleoenvironments and climate

Paleoenvironmental reconstructions for the Barstovian indicate a mosaic of habitats, including open woodlands, grassland-savanna mosaics, and riparian corridors preserved in formations like the Ash Hollow Formation and Cook Ranch Formation. Paleobotanical and isotopic studies by teams at University of Arizona, Ohio State University, and University of Washington use pollen, leaf physiognomy, and stable isotopes to infer climates transitioning toward greater aridity and seasonality, paralleling global trends documented by cores from Ocean Drilling Program and International Ocean Discovery Program. Climatic shifts during the Barstovian also correspond with faunal turnover observed in faunas comparable to those from the Siwaliks and European Mammal Neogene records.

Faunal assemblages and notable taxa

Barstovian faunas are characterized by diverse mammals including proboscideans, perissodactyls, artiodactyls, carnivorans, rodents, and insectivores. Notable large mammals often cited include gomphotheres documented in collections at the Natural History Museum, Los Angeles County, oreodonts known from the American Museum of Natural History, and equids described in monographs from University of California Museum of Paleontology. Predators such as amphicyonids and felids appear alongside taxa like Nannippus, Merychippus, Aepycamelus, Teleoceras, and Daeodon, with smaller taxa represented by genera studied at Harvard University, University of Texas at Austin, and Field Museum of Natural History. Fossil sites yielding Barstovian assemblages include the Agate Fossil Beds National Monument, Ashfall Fossil Beds State Historical Park, and the John Day Fossil Beds National Monument.

Biostratigraphic significance and correlation

The Barstovian serves as a key biostratigraphic unit within the NALMA framework for correlating North American localities and for intercontinental comparisons with European and Asian mammal zones such as the Astaracian and European Mammal Neogene subdivisions. Correlation efforts utilize index taxa recorded in faunal lists curated by the Paleobiology Database, studies from the Society of Vertebrate Paleontology, and syntheses published in outlets associated with Geological Society of America and Palaeontology. Magnetostratigraphic ties to chrons like Chron C5 and radiometric constraints from tuffs analyzed at Argonne National Laboratory refine Barstovian correlations with global stages like the Langhian.

History of research and naming

The name derives from work on type sections and fossil localities first described in the early 20th century by paleontologists connected to the California Institute of Technology, University of California, and University of Nebraska State Museum. Subsequent revisions and formalizations were produced by researchers at the Smithsonian Institution, Harvard University, and American Museum of Natural History, with stratigraphic boundaries adjusted following magnetostratigraphic and radiometric advances by teams from USGS and Lamont–Doherty Earth Observatory. Major syntheses and faunal lists were compiled in monographs and conference volumes sponsored by the International Union of Geological Sciences and the Society of Vertebrate Paleontology.

Category:Miocene North America