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| Chañares Formation | |
|---|---|
| Name | Chañares Formation |
| Type | Geological formation |
| Period | Triassic |
| Primary lithology | Sandstone, mudstone, conglomerate |
| Otherlithology | Volcaniclastic tuff, ash |
| Region | La Rioja Province, San Juan Province |
| Country | Argentina |
| Unitof | Ischigualasto-Villa Unión Basin |
| Thickness | ~300–500 m |
Chañares Formation is a Middle Triassic continental rock succession in northwestern Argentina, known for exceptionally preserved tetrapod fossils and volcanic tuffs. The formation crops out in the Ischigualasto-Villa Unión Basin and has been central to debates about early archosaur evolution and Triassic paleoecology in Gondwana. Work on the unit has involved field teams from University of Buenos Aires, Museo de La Plata, Smithsonian Institution, University of Chicago, and National Geographic Society.
The formation overlies the Tarjados Formation and underlies the Los Rastros Formation within the Ischigualasto-Villa Unión Basin, showing a vertical succession of fluvial sandstones, channel conglomerates, fine-grained mudstones, and multiple volcanic tuff layers. Regional mapping by researchers associated with Instituto y Museo de Ciencias Naturales and Consejo Nacional de Investigaciones Científicas y Técnicas correlated these strata across exposures near Talampaya National Park, La Rioja Province, and Ischigualasto Provincial Park, integrating biostratigraphic ties to units described by teams from Universidad Nacional de San Juan and Universidad Nacional de La Plata. Petrographic studies linked detrital compositions to provenance in the Sierras Pampeanas and volcanic input consistent with rhyolitic ash chemistry analyzed by collaborators from Smithsonian Institution and University of São Paulo.
Radiometric dates from volcanic tuffs using U–Pb zircon geochronology by groups including University of Arizona and University of Buenos Aires place the unit in the late Early to Middle Triassic (Anisian–Ladinian), with key ages around ~236–234 Ma. These results refined earlier biostratigraphic correlations based on comparative assemblages with the Dinodontosaurus Assemblage Zone and with Gondwanan units studied by teams at University of Cape Town, Monash University, and Museo Argentino de Ciencias Naturales. High-precision isotopic work integrated efforts from Los Alamos National Laboratory and Australian National University to resolve diachronous deposition and reconcile magnetostratigraphic data compiled by researchers from Purdue University and University of California, Berkeley.
Sedimentological analyses by field parties from Universidad Nacional de La Plata, University of Chicago, and University of Texas at Austin interpret the formation as an alluvial to fluvial-dominated system with episodic overbank flooding, palaeosol development, and pyroclastic input from nearby volcanic centers. Facies models compared by scholars at University of Cambridge, University of Oxford, and University of São Paulo emphasize braided to meandering channels, distal floodplain fines, and ash-fall events that influenced plant and vertebrate habitats. Paleoecological reconstructions drawing on collaborations with American Museum of Natural History, Natural History Museum, London, and Museo de La Plata argue for a seasonally variable climate within the Pangea supercontinent, analogous to settings examined by teams from University of Zurich and University of Buenos Aires.
The formation yields a diverse vertebrate assemblage including early archosaurs, proterosuchids, cynodonts, dicynodonts, and putative rauisuchians, with notable taxa described by researchers at Museo de La Plata, Smithsonian Institution, University of Chicago, and Museo Argentino de Ciencias Naturales. Iconic genera and species recovered from these beds were revised in monographs produced by scholars from Universidad Nacional del Comahue, University of São Paulo, University of Zurich, and Universidad Nacional de San Juan, and compared to contemporaneous faunas from South Africa and Antarctica by teams from University of Cape Town and British Antarctic Survey. Plant remains, invertebrate traces, and coprolites studied by scientists at Royal Ontario Museum and Universidad Nacional de La Plata complement vertebrate data to inform trophic dynamics and community structure.
Exceptional preservation in ash-rich horizons has been examined by taphonomists from Smithsonian Institution, University of Buenos Aires, and Universidad Nacional de La Plata, who documented rapid burial in pyroclastic flows and lahar-related deposits leading to articulated skeletons and articulated cranial material. Experimental and microsedimentological work by researchers at University of Chicago and Australian National University linked mineralogical signatures to diagenetic pathways influenced by volcaniclastic input, while studies by Museo Argentino de Ciencias Naturales and Instituto de Geología y Recursos Minerales characterized compaction, geochemical alteration, and microbial role in preservation.
The formation was named and first described in regional geological surveys conducted by Argentine geologists associated with Servicio Geológico Minero Argentino and early paleontological work at Museo de La Plata in the mid-20th century. Subsequent major contributions came from expeditions funded by National Geographic Society and institutions such as Smithsonian Institution, leading to pivotal monographs by researchers at Universidad Nacional de La Plata, University of Chicago, and Museo Argentino de Ciencias Naturales. International collaborations involving University of Buenos Aires, Universidad Nacional de San Juan, and University of São Paulo have continued to refine taxonomic concepts, stratigraphic frameworks, and chronostratigraphic placement, securing the unit's status in Triassic paleobiology literature.
Category:Geologic formations of Argentina