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| Paso del Sapo Formation | |
|---|---|
| Name | Paso del Sapo Formation |
| Type | Geological formation |
| Period | Cenozoic |
| Age | Eocene–Oligocene (proposed) |
| Region | Chubut Province, Argentina |
| Country | Argentina |
| Namedfor | Paso del Sapo |
Paso del Sapo Formation The Paso del Sapo Formation is a Cenozoic stratigraphic unit in northern Chubut Province, Argentina known for continental fluvial and lacustrine deposits that preserve vertebrate fossils and plant remains. Located in the foreland of the southern Andes, the unit records sedimentary responses to Paleogene tectonism and climate change in Patagonia. Research on the formation links regional studies of the Golfo San Jorge Basin, Deseado Massif, and Andean uplift history with paleobiological work on Eocene–Oligocene faunas.
The formation has been studied within the context of Patagoniaan stratigraphy, regional basin analysis, and vertebrate paleontology, connecting work conducted by institutions such as the Museo Paleontológico Egidio Feruglio, Universidad Nacional de la Patagonia, and international teams from the Smithsonian Institution. Fieldwork often integrates mapping by the Servicio Geológico Minero Argentino and collaborations with researchers associated with the Consejo Nacional de Investigaciones Científicas y Técnicas.
Paso del Sapo strata overlie older Paleozoic and Mesozoic rocks exposed in the eastern foothills of the Andes and interfinger with coeval Cenozoic units correlated across the Golfo San Jorge Basin and the Neuquén Basin. Stratigraphic sections show alternations of channelized and overbank deposits that have been correlated using biostratigraphic markers and magnetostratigraphic work similar to studies in the Colhue Huapi Formation and Sarmiento Formation. Regional tectonostratigraphic models tie deposition to flexural loading during Andean orogenesis and to sediment supply changes documented in studies of the Pampean and Patagonian forelands.
Lithologies are dominated by sandstones, siltstones, mudstones, and localized conglomerates interpreted as fluvial point-bar, crevasse-splay, and overbank facies. Paleosol horizons and lignite-bearing levels indicate episodic floodplain stability comparable to facies described in the Sierra de la Ventana and Río Chico Group. Sedimentological analyses reference channel dimensions, paleocurrent indicators, and grain-size distributions similar to those used in basin studies at the Mata Amarilla Formation and in the Chubut River catchment.
Fossil assemblages include mammals, reptiles, amphibians, freshwater fish, and plant remains that contribute to understanding Paleogene biogeography of South America. Vertebrate remains have been compared to taxa known from the Deseadan and Colhuehuapian South American Land Mammal Ages and to faunas described from the Sarmiento Formation and Chubut Group. Plant macrofossils and palynomorphs provide links to floras recorded in Antarctica and Australia during Paleogene greenhouse intervals. Paleontological work has involved curatorial and descriptive contributions from the Museo Argentino de Ciencias Naturales and international collaborations with universities such as Harvard University and University of California, Berkeley.
Interpretations favor a Paleogene age, spanning late Eocene into Oligocene intervals, based on mammalian biostratigraphy, palynology, and regional correlations with dated units like the Sarmiento Formation. Paleoenvironmental reconstructions indicate a warm-temperate to subtropical climate transitioning toward cooler and more seasonal conditions during the Oligocene, reflecting global changes documented in studies of the Eocene–Oligocene transition and in isotopic records from the Southern Ocean. Depositional environments are reconstructed as meandering to braided fluvial systems with intercalated floodplain lakes and swamps akin to settings inferred for the Deseado Massif basinal deposits.
Although not a major hydrocarbon target compared with the Neuquén Basin or Golfo San Jorge Basin main plays, the formation contributes to hydrogeological frameworks, alluvial aggregate resources, and paleontological heritage that supports regional geotourism and museum collections. Scientifically, Paso del Sapo provides data relevant to hypotheses about South American mammal evolution, Paleogene climate change, and the timing of Andean uplift, complementing isotopic work from ice cores and marine records held by the National Oceanic and Atmospheric Administration and comparative studies at institutions like the British Geological Survey.
Exposures occur near the town of Paso del Sapo and along tributaries of the Chubut River, with outcrops accessible from provincial roads and river valleys that enable stratigraphic logging and fossil prospecting. The unit is mapped within northern Chubut Province and extends into adjacent sectors where equivalent facies have been identified near the Sierra del Mecanico and other local relief elements that control preservation and exposure.
Initial descriptions and the naming of the unit derive from regional geological surveys and paleontological fieldwork during the mid-20th century, building on earlier reconnaissance by geologists associated with the Servicio Geológico Nacional and naturalists visiting the Patagonian interior. Subsequent revisions and detailed studies have been published by researchers affiliated with the Universidad Nacional de la Plata, the Consejo Nacional de Investigaciones Científicas y Técnicas, and international teams, refining its stratigraphic limits, age assignments, and paleoenvironmental interpretations in concert with advances in magnetostratigraphy, palynology, and vertebrate taxonomy.
Category:Geologic formations of Argentina Category:Paleogene geology