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| Bahía Inglesa Formation | |
|---|---|
| Name | Bahía Inglesa Formation |
| Type | Geological formation |
| Period | Neogene |
| Age | Miocene–Pliocene |
| Region | Atacama Region |
| Country | Chile |
Bahía Inglesa Formation is a Neogene marine sedimentary succession exposed along the northern coast of the Atacama Desert in the Atacama Region of northern Chile. The unit has been the focus of multidisciplinary studies involving paleontology, stratigraphy, and sedimentology and has yielded abundant vertebrate and invertebrate fossils that illuminate Pacific faunal turnover during the Miocene and Pliocene. Work on the formation intersects research conducted by institutions such as the Universidad de Chile, Universidad Católica del Norte, Smithsonian Institution, and the Natural History Museum, London.
The formation crops out near coastal localities including Caldera, Huasco, and the coastal platform adjacent to the Bahía Inglesa bay, within the broader tectonic framework shaped by the Nazca Plate–South American Plate convergent margin. Regional structure is influenced by the nearby Atacama Fault System and Neogene uplift associated with the Andean orogeny, with exposures adjacent to the Chañaral Bay and the Copiapó River mouth. Stratigraphically it overlies older Cretaceous and Paleogene units such as the Cerro Ballena beds and is juxtaposed with Quaternary deposits along the coastal scarp.
Lithologies include well-sorted sandstones, silty sandstones, conglomerates, and calcareous concretions, as well as phosphatic layers and tuffaceous horizons correlated to episodes of volcanism in the region. The succession exhibits multiple transgressive–regressive cycles preserved as marine parasequences, with lateral facies changes evident toward the Chile Rise-ward margin. Key marker beds used for correlation include phosphorite-rich horizons and bentonitic layers tied to regional ash-fall from volcanic centers such as the Altiplano-Puna volcanic complex.
The formation is renowned for its diverse marine vertebrate assemblage, including fossil remains of penguins, pinnipeds, cetaceans, and teleost fishes documented alongside rich invertebrate faunas of bivalves, gastropods, echinoids, and crustaceans. Notable discoveries include fossil cetaceans linked to forms compared with taxa described from the Paraná Basin and the Pisco Formation of Peru, penguin remains comparable to those from New Zealand and Antarctica, and pinniped specimens informing pinniped evolution relative to taxa from the California and South African coasts. Paleontologists and institutions such as Museo Nacional de Historia Natural (Chile), Field Museum of Natural History, and researchers affiliated with the University of California, Berkeley have described numerous taxa from the unit.
Biostratigraphic and radiometric constraints place the succession mainly within the Miocene to Pliocene epochs of the Neogene, with age models calibrated using microfossil assemblages such as foraminifera and nannofossils correlated to the South American Land Mammal Ages framework and magnetostratigraphy tied to the geomagnetic polarity timescale. Detrital zircon geochronology and K–Ar dating of interbedded tuffs have been applied in studies involving collaborations between the University of Oxford, Universidad de Concepción, and regional geological surveys.
Sedimentological and paleoecological evidence indicates deposition in a shallow to outer neritic marine setting influenced by upwelling associated with the Humboldt Current system and fluctuating nutrient levels that promoted phosphogenesis. Paleoecological reconstructions draw on comparisons with the modern Peru–Chile Trench ecosystem and Pliocene warming events considered alongside records from the Pisco Basin and Tortonian–Messinian transitional sequences. Taphonomic work on bonebeds and shell concentrations has informed interpretations of carcass accumulation processes and storm-related assemblage reworking.
Phosphatic horizons within the succession have been of economic interest, analogous to phosphate deposits exploited elsewhere along the Peruvian coastal desert and within the Atacama Desert margin. The mineralization has implications for regional fertilizer-resource assessments and links to historical mining activities centered near Caldera and industrial processing facilities operated by companies historically active in the region. The formation’s sand and gravel resources have also been utilized locally for construction aggregates.
Scientific work on the unit began with early 20th-century geological surveys by expeditions tied to institutions such as the United States Geological Survey and Chilean national surveys, with subsequent major contributions from paleontologists and stratigraphers affiliated with the Universidad de Chile, Universidad de Antofagasta, Smithsonian Institution, Natural History Museum, London, Field Museum, and international universities including University of California, Los Angeles and University of Cambridge. Notable monographs and papers have addressed vertebrate paleontology, phosphogenesis, and sequence stratigraphy, producing a robust literature that situates the unit within broader Neogene Pacific history and links it to contemporaneous units such as the Pisco Formation and the Gaiman Formation.
Category:Geologic formations of Chile Category:Miocene geology Category:Pliocene geology Category:Atacama Region