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| Sarmiento Formation | |
|---|---|
| Name | Sarmiento Formation |
| Type | Geological formation |
| Period | Paleogene–Neogene |
| Region | Chubut Province, Santa Cruz Province |
| Country | Argentina |
| Namedfor | Sarmiento |
Sarmiento Formation is a fossiliferous geological unit in central and southern Patagonia of Argentina notable for preserving a diverse record of Paleogene to Neogene terrestrial life and continental sedimentation. Important for studies in paleontology, stratigraphy, and paleoclimatology, it has produced key vertebrate assemblages that inform regional biostratigraphic correlations and global discussions about Cenozoic faunal turnover. Work on the unit has involved researchers affiliated with institutions such as the Museo Argentino de Ciencias Naturales and the Smithsonian Institution and has influenced interpretations of South American land mammal ages used by teams at the University of Buenos Aires and the American Museum of Natural History.
The unit crops out across the central Chubut Province and northern Santa Cruz Province and lies within tectonic domains influenced by the Andean orogeny and intraplate basins such as the Golfo San Jorge Basin and the Río Chico Basin. Structural relationships show synsedimentary faulting correlated with flexural responses to Andean uplift events recognized in stratigraphic studies by groups at the Comisión Nacional de Energía Atómica and the Servicio Geológico Minero Argentino. Regional mapping projects tied to the Instituto Geográfico Nacional have documented thickness variations and lateral facies changes that relate to basin subsidence histories and paleodrainage systems linked to basins studied by the International Geological Correlation Programme.
Stratigraphic subdivisions of the unit are correlated with South American land mammal ages such as the Divisaderan, Mustersan, Tinguirirican, Deseadan, and Colhuehuapian; those correlations rely on vertebrate biostratigraphy and radiometric constraints provided by teams at the Geological Survey of Argentina. Magnetostratigraphic work and ^40Ar/^39Ar dating from tuffs tied to laboratories at the University of California, Berkeley and the Instituto de Geocronología y Geoquímica Isotópica have refined its age range from the middle Eocene through the early Miocene. Correlations to units such as the Gaiman Formation and the Chubut Formation have been debated in syntheses produced by researchers at the University of Zaragoza and the Natural History Museum, London.
Lithofacies include continental fluvial sandstone, overbank mudstone, tuffaceous ash layers, paleosol horizons, and occasional conglomerate beds; analyses published by teams at the Universidad Nacional del Comahue and the CONICET emphasize lateral facies stacking patterns indicative of alluvial plain and proximal-axial fluvial systems. Petrographic work involving the Argentine Institute of Petroleum and geochemical provenance studies tied to the University of Buenos Aires demonstrate variable input from proximate plutonic and metamorphic source areas uplifted during episodes related to the Andean uplift. Primary sedimentary structures such as trough cross-bedding, planar laminations, paleocurrent indicators, calcrete horizons, and lateritization features have been used by sedimentologists from the University of Oxford and the University of Chicago to reconstruct channel avulsion dynamics and soil-forming intervals.
The unit is celebrated for its exceptionally rich vertebrate paleofauna, including diverse notoungulates, astrapotheres, litopterns, xenarthrans (sloths and armadillos), cingulates, phorusrhacids, and early caviomorph rodents; collections have been described by paleontologists associated with the Museo Paleontológico Egidio Feruglio, the American Museum of Natural History, and the Field Museum of Natural History. Notable taxa documented in systematic treatments include representatives comparable to members of families such as the Notoungulata, Astrapotheria, Litopterna, and predatory birds related to the Phorusrhacidae clade, with specimens curated in repositories including the Museo de La Plata and the Natural History Museum, Paris. Paleobotanical remains, including fossil wood and leaf impressions, have been analyzed by researchers at the Royal Botanic Gardens, Kew and the Smithsonian Tropical Research Institute to document changes in plant assemblages concurrent with mammalian turnover. Collaboration between teams from the University of Michigan and the Universidad Nacional de La Plata has produced revisions to taxonomic frameworks and phylogenetic hypotheses that bear on continental biogeography and endemism during Cenozoic intervals.
Facies associations and paleosol morphologies support interpretation as fluvial to overbank alluvial plain systems with intervals of reduced sedimentation that allowed soil formation and volcanic ash accumulation, a model advanced in joint studies by the Universidad Nacional de Río Negro and the Universidad Nacional del Comahue. Stable isotope work on fossil enamel and pedogenic carbonates undertaken at the Max Planck Institute for Chemical Ecology and the University of Bonn indicates climatic shifts from more mesic, warm conditions in the Eocene toward cooler, more seasonal climates by the Oligocene–Miocene transition, paralleling global cooling events recognized by researchers at the National Oceanic and Atmospheric Administration and the Paleoclimate Modelling Intercomparison Project. Vegetation change documented by palynological analyses from teams at the Universidad Nacional de La Plata and the Royal Society highlights transitions from mixed forest to more open woodland-grassland mosaics, affecting herbivore adaptations and community composition noted in faunal studies by the American Museum of Natural History.
Beyond its scientific value for reconstructing South American Cenozoic ecosystems, the unit has implications for regional hydrogeology and unconventional resource assessment investigated by corporate and academic groups including the Yacimientos Petrolíferos Fiscales research units and the Argentine Institute of Petroleum. Fossil localities have driven development of paleontological tourism and outreach programs coordinated with the Gobierno de Chubut and cultural institutions such as the Museo Provincial Carlos Ameghino. Ongoing multidisciplinary research involving institutions like the CONICET, the Smithsonian Institution, and international universities continues to refine models of Cenozoic evolution, continental faunal interchange, and responses of terrestrial ecosystems to climatic forcing events cataloged by the Intergovernmental Panel on Climate Change.
Category:Geologic formations of Argentina Category:Paleontology in Argentina