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| Abanico Formation | |
|---|---|
| Name | Abanico Formation |
| Type | Geological formation |
| Period | Oligocene–Miocene |
| Prange | Paleogene–Neogene |
| Region | Central Chile, Andes |
| Country | Chile |
Abanico Formation is a major Paleogene–Neogene siliciclastic and volcaniclastic succession exposed in the central Chilean Andes. The unit records synorogenic basin fill linked to Andean tectonics and preserves abundant fossil assemblages, volcanic products, and economically relevant mineralization. It is widely studied in fields such as stratigraphy, sedimentology, paleontology, and tectonics.
The formation crops out along the Principal Cordillera near Santiago, Chile, Valparaíso Region, and extends toward the Maule Region, forming part of the Andean orogenic architecture influenced by the interaction of the Nazca Plate, South American Plate, and remnant microplates such as the Juan Fernández Ridge and the Inca Plateau. Regional correlations have been drawn with contemporaneous basins like the Magallanes Basin and the Pampean flat-slab segment influenced by changes in subduction geometry documented in studies tied to the Andean uplift and the Central Andes uplift events. Volcanism contemporaneous with deposition links the succession to episodes comparable to those recorded at volcanic centers such as Cerro Azul, Copahue, and Descabezado Grande.
The succession comprises multiple members and informal units that sit above older basement rocks including the Farellones Formation and intrude or are overlain by Neogene volcanic and plutonic rocks such as the Abanico intrusive suite and the Cordillera Principal plutons. Lithostratigraphic subdivisions correlate with magnetostratigraphy, biostratigraphy using fossil mammals and gastropods, and radiometric dates from interbedded tuffs tied to the K–Ar dating and Ar–Ar dating chronologies. Key stratigraphic markers include prominent tuff horizons and coarse conglomerate beds that permit correlation across synclines and anticlines adjacent to structural features such as the San Ramón Fault and the Genex Fault Zone.
Depositional ages span much of the Oligocene through the Miocene, constrained by radiometric ages, magnetostratigraphic polarity reversals, and biostratigraphic ties to fossil assemblages comparable to those in the South American Land Mammal Ages framework such as Deseadan and Santacrucian. Paleoenvironmental reconstructions indicate a transition from fluvial and lacustrine settings to deltaic and shallow marine incursions reflecting tectonic uplift, climatic shifts tied to the Miocene Climatic Optimum, and changes in sediment supply associated with the subduction rate variations during the Neogene.
The unit consists predominantly of volcaniclastic sandstones, mudstones, tuffs, and conglomerates with interbeds of andesitic to rhyolitic ash-fall deposits linked to regional centers like Llaima and Villarrica. Grain-size trends, foreset cross-bedding, and channel-fill geometries document braided to meandering fluvial systems and proximal alluvial fans associated with active uplift along structures comparable to the Frontal Cordillera and the Precordillera. Authigenic minerals and diagenetic fronts record burial histories comparable with burial diagenesis models used in basins such as the Neuquén Basin.
Fossil content includes mammals, birds, reptiles, freshwater molluscs, and plant macrofossils that allow interbasinal correlation with faunas from Patagonia, Peru, and the Andean Foreland Basin. Notable vertebrate remains have affinities to taxa familiar from the Deseadan and Santacrucian assemblages with implications for paleobiogeography discussed alongside records from the Santa Cruz Formation and the Itaboraí Formation. Palynological data and leaf macrofossils inform reconstructions of Oligocene–Miocene floras comparable to those documented in the Petrified Forest of Sarmiento and in sites studied by paleobotanists affiliated with institutions such as the Museo Nacional de Historia Natural (Chile).
Sedimentation occurred within a flexural and piggyback basin system driven by Andean shortening and magmatism tied to episodic changes in subduction angle, comparable to flat-slab episodes that affected regions near the Sierras Pampeanas and the Peruvian Andes. Synsedimentary deformation, growth strata, and synorogenic clastic wedges record progressive uplift of the hinterland and emplacement of intrusive complexes analogous to the Coihaique Complex. The evolution of the basin has been integrated into tectonic reconstructions involving plate kinematics studies employing data from the Pacific Plate–Nazca Plate interactions and the reorganization events contemporaneous with the rise of the Andean Plateau.
The formation hosts aggregate resources used in construction near urban centers such as Santiago, Chile and contains volcanic ash layers that have been investigated for use in pozzolanic materials and soil amendments in agricultural areas like the Central Valley (Chile). Local hydrogeological studies consider Abanico strata as aquifer units in catchments supplying communities around the Maipo River and Aconcagua River, while mineralization associated with syntectonic hydrothermal systems has been explored in contexts comparable to epithermal veins found near mining districts like El Teniente and El Indio.
Category:Geologic formations of Chile Category:Oligocene geology Category:Miocene geology