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| Oxaya Formation | |
|---|---|
| Name | Oxaya Formation |
| Period | Oligocene–Miocene |
| Type | Geological formation |
| Region | Arica y Parinacota Region |
| Country | Chile |
| Namedfor | Oxaya |
Oxaya Formation is a Neogene siliciclastic succession exposed in the highlands of northern Chile, notable for its record of Oligocene–Miocene sedimentation within the Andean Cordillera. Distributed across parts of the Arica y Parinacota Region and the Tarapacá Region, the formation records interactions between volcanism, basin subsidence, and tectonism during the development of the Central Andes. Its sediments have been studied in relation to regional uplift, basin inversion, and the evolution of the Andean orogeny.
The formation crops out along the western slopes of the Andes in northern Chile and lies within the broader tectonostratigraphic framework that includes the Altiplano, the Puna (plateau), and adjacent forearc and backarc provinces. Regional mapping links the succession to surface expressions around the towns of Arica, Iquique, and the Oxaya plateau. Geological investigations have integrated field mapping, stratigraphic logging, geochronology, and structural analysis to place the unit within the Oligocene–Miocene chronostratigraphic scheme used across South American Cenozoic basins such as the Intermontane basins of the Central Andes.
Stratigraphically, the Oxaya Formation overlies older Mesozoic and Paleogene units and is in turn overlain by younger Miocene volcanic and sedimentary sequences related to Andean volcanism. Correlations have been attempted with coeval units in the Bolivian Altiplano, the Puna, and the coastal basins of northern Chile. Biostratigraphic and radiometric constraints tie deposition to a time interval contemporaneous with regional tectonic events including phases recognized in the stratigraphic records of the Loa River basin and the Coastal Cordillera.
The succession is dominated by reddish to brownish conglomerates, sandstones, and mudstones with interbedded tuffs and volcaniclastics that record proximal to distal depositional processes. Provenance studies invoke source areas within uplifted Paleogene and Mesozoic complexes such as outcrops related to the Cordillera de la Costa and remnant exposures of the Paleozoic basement in northern Chile. Petrographic analyses identify clastic grains including feldspar and lithic fragments derived from granitoid and volcanic source terrains comparable to those mapped in the Coquimbo Region and Antofagasta Region.
Although primarily siliciclastic and volcaniclastic, the formation locally preserves vertebrate and plant remains that have been used for biostratigraphic correlation with other Neogene faunas of South America, including assemblages compared with specimens from the Bolivian Altiplano and the Pampean region. Paleobotanical fragments, pollen, and rare freshwater mollusks provide paleoenvironmental and paleoclimatic signals tied to wider Neogene shifts recorded in the fossil archives of the Atacama Desert margins and the Central Andes. Fossil evidence has been incorporated into broader syntheses with Miocene records from sites such as Tertiary basins of Patagonia.
Sedimentation reflects a range from alluvial fan and fluvial systems to distal floodplain and lacustrine settings influenced by contemporaneous volcanism. Facies analysis indicates deposition within intermontane basins and proximal foreland settings responding to crustal loading and flexural subsidence associated with the progressive growth of the Andean orogeny. Volcaniclastic layers testify to nearby volcanic centers active in the Neogene, akin to volcanic histories reconstructed for provinces like the Central Volcanic Zone.
The Oxaya Formation records synorogenic deposition linked to shortening, uplift, and strike-slip reorganization within northern Chile. Deformation styles include folding, reverse faulting, and local thrust imbrication, consistent with regional structural trends observed along the western edge of the Altiplano-Puna plateau. Kinematic studies relate strain patterns to plate interactions at the Peru–Chile Trench and stresses induced by changes in subduction geometry and slab dynamics such as those affecting the Nazca Plate–South American Plate boundary.
While not a primary hydrocarbon target, the Oxaya Formation and adjacent Neogene successions are relevant for groundwater resources, aggregate extraction, and as host strata for placer and alluvial mineral concentrations exploited in the Arica and Parinacota Region. Its stratigraphic and structural characteristics inform mineral exploration strategies for base metals and influence infrastructure planning for transport corridors linking Arica with inland mining districts. Paleoclimatic and tectonic insights drawn from the formation contribute to regional geomorphologic and geohazard assessments important to agencies such as the Servicio Nacional de Geología y Minería.
Category:Geologic formations of Chile Category:Neogene South America