Bartonian
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| Bartonian | |
|---|---|
| Name | Bartonian |
| Color | #a0a8ff |
| Time start | 41.2 |
| Time end | 37.8 |
| Time unit | million years ago |
| Formal | Formal |
| Usage | Global (ICS) |
| Chrono unit | Age |
| Strat unit | Stage |
| Timespan formal | Bartonian Stage of the Middle Eocene |
Bartonian The Bartonian is a middle Eocene chronostratigraphic stage formally recognized by the International Commission on Stratigraphy and used in global lithostratigraphic practice. It is widely employed in regional mapping, stratigraphic correlation, and paleoenvironmental reconstruction by stratigraphers and paleontologists working on Tertiary successions across Europe, North America, Asia, Africa, and Australasia. Stratigraphic schemes and paleoclimate syntheses published by researchers at institutions such as the Natural History Museum, the British Geological Survey, and the United States Geological Survey frequently reference Bartonian successions.
Definition and Stratigraphic Context
The Bartonian stage was originally defined based on lithostratigraphic and biostratigraphic criteria from classic sections in the Paris Basin, the London Basin, and regions of southern England, with early descriptive work by geologists associated with the Geological Society of London and the Société Géologique de France. The stratotype guidance and boundary definitions have been refined through correlation efforts involving the International Commission on Stratigraphy, the International Union of Geological Sciences, and regional geological surveys including the British Geological Survey and Service géologique national. Key marker horizons used to delimit the Bartonian include calcareous nannofossil assemblages, planktonic foraminiferal datum events, and isotopic excursions recognized in sections studied by researchers at institutions such as the University of Cambridge, the University of Strasbourg, and the Royal Belgian Institute of Natural Sciences.
Age and Chronostratigraphy
The Bartonian is conventionally placed between approximately 41.2 and 37.8 million years ago, situated within the middle Eocene Epoch of the Paleogene Period. Chronostratigraphic placement relies on integration of magnetostratigraphy, astrochronology, and radiometric calibration from volcanic ash layers correlated by laboratories at institutions including the Lamont–Doherty Earth Observatory, the Scripps Institution of Oceanography, and the U.S. Geological Survey. Global Geological Time Scale panels convened by the International Commission on Stratigraphy and published syntheses by the Geological Society of America provide the standard numerical ages and tie the Bartonian to adjacent stages such as the Lutetian below and the Priabonian above. High-resolution age models for Bartonian successions have been informed by cyclostratigraphic work from research groups at the University of Oxford and Utrecht University.
Regional and Global Correlations
Bartonian strata have been recognized and correlated across Europe (notably France, United Kingdom, Belgium), North America (Gulf Coastal Plain, southeastern United States), North Africa (Morocco, Tunisia), the Middle East (Iran, Turkey), Central Asia (Kazakhstan, Russia), South Asia (India, Pakistan), and Australasia (Australia, New Zealand). Paleontologists and stratigraphers use faunal lists and nannofossil zonations developed by researchers at institutions such as the Natural History Museum London, the Smithsonian Institution, and the Muséum national d'Histoire naturelle to correlate Bartonian units with regional stages like the North American Uintan and Clarkforkian regional frameworks. Marine Bartonian successions are correlated with ocean drilling records from the Ocean Drilling Program and International Ocean Discovery Program, where cores analyzed by teams at Texas A&M University and the Japan Agency for Marine-Earth Science and Technology provide cross-ocean ties.
Paleoenvironments and Climate
Paleoenvironmental reconstructions for Bartonian intervals indicate warm greenhouse conditions punctuated by regional variability, inferred from stable isotope studies, palynology, and paleobotanical assemblages reported by researchers at institutions such as the University of Göttingen, the Swedish Museum of Natural History, and the University of California, Berkeley. Marine Bartonian deposits include calcareous shelf carbonates, siliceous mudstones, and hemipelagic marls that record eustatic fluctuations and regional upwelling influenced by tectonics involving plate boundaries studied by geoscientists at the European Geosciences Union and the American Geophysical Union. Terrestrial Bartonian floras and coal-bearing sequences from basins investigated by the British Geological Survey and the Indian Statistical Institute suggest subtropical to warm-temperate forests with diverse angiosperm, gymnosperm, and ferns assemblages, while isotope excursions and modeled CO2 reconstructions produced by groups at ETH Zurich and the Max Planck Institute for Chemistry indicate elevated greenhouse gas levels relative to preindustrial values.
Biostratigraphy and Fossil Assemblages
Bartonian biostratigraphy relies heavily on planktonic foraminifera zonations, calcareous nannofossil bioevents, and benthic foraminiferal turnovers documented by researchers at the Natural History Museum, the University of Vienna, and the Paleontological Institute of Moscow. Marine fossil assemblages include diverse foraminifera, ostracods, nannoplankton, echinoderms, and mollusks documented in classic localities studied by teams from the University of Lyon and the University of Barcelona. Terrestrial vertebrate faunas assigned to Bartonian-equivalent deposits feature early primates, ungulate lineages, and creodonts described in museum collections at the American Museum of Natural History, the Smithsonian Institution, and the Natural History Museum of Paris. Paleobotanical records, palynological spectra, and insect compression fossils curated at the Deutsches Entomologisches Institut and the Royal Ontario Museum provide additional biostratigraphic markers used for regional correlation.
Geological Significance and Usage
The Bartonian stage is a key interval for understanding middle Eocene Earth systems, including the evolution of modern mammal orders, the development of Eocene greenhouse climates, and marine biotic turnovers documented in stratigraphic compilations by the International Commission on Stratigraphy and the Geological Society. It is used routinely in basin analysis, hydrocarbon exploration in provinces evaluated by industry groups such as Schlumberger and BP, and academic studies published through journals associated with the American Association of Petroleum Geologists and the Geological Society of America. Bartonian successions continue to serve as reference intervals for paleoclimate modeling conducted by teams at institutions such as NASA Goddard Institute for Space Studies and the European Centre for Medium-Range Weather Forecasts.