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| Loncoche Formation | |
|---|---|
| Name | Loncoche Formation |
| Type | Geological formation |
| Period | Late Jurassic–Early Cretaceous |
| Region | Araucanía Region, Los Ríos Region, Maule Region |
| Country | Chile, Argentina |
| Underlies | Quiriquina Formation |
| Overlies | Trafún Metamorphic Complex |
Loncoche Formation The Loncoche Formation is a lithostratigraphic unit in south-central Chile and adjacent Argentina known for volcanic, sedimentary, and fossiliferous sequences preserved across the Araucanía Region, Los Ríos Region, and Maule Region. Geologists and paleontologists working with institutions such as the Comisión Chilena del Cobre, the Universidad de Chile, the Universidad Austral de Chile, and the Museo Nacional de Historia Natural (Chile) have documented its stratigraphy, lithology, and paleobiota, correlating units with the Tithonian to Berriasian intervals recognized in regional chronostratigraphy. The formation has been cited in studies by researchers affiliated with the Servicio Nacional de Geología y Minería (SERNAGEOMIN), the Instituto Geográfico Militar (IGM), and international collaborators at the University of Buenos Aires and the Smithsonian Institution.
The Loncoche succession crops out along structural features tied to the Andean orogeny and the Patagonian Andes foreland, intersecting with mapped belts such as the Coihaique Belt and the Chiloé Block. Structural analyses reference tectonostratigraphic elements described by the Servicio Nacional de Geología y Minería (Chile) and models from the Andean Cordillera research community, including comparisons with the Chilenia Terrane and the North Patagonian Massif. Regional mapping integrates datasets from the Instituto Geográfico Militar (Argentina) and basin studies tied to the Neuquén Basin and the Arauco Basin.
Stratigraphic frameworks position the Loncoche unit above metamorphic basement units linked to the Trafún Metamorphic Complex and beneath marine overlays like the Quiriquina Formation, with lateral facies transitions toward sequences correlated with the Toqui Formation and the Cañadón Asfalto Formation. Chronostratigraphic work references ammonite- and palynomorph-based correlations used by researchers at the Universidad Nacional del Comahue and the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Stratigraphers employ techniques consistent with conventions from the International Commission on Stratigraphy and regional charts produced by SERNAGEOMIN.
The formation comprises interbedded volcaniclastic sandstones, tuffs, siltstones, and conglomerates with accessory lithologies including lapilli tuff and volcanic breccia, described in petrographic studies at the Universidad de Concepción and the Pontificia Universidad Católica de Chile. Mineralogical assemblages feature phenocrysts of plagioclase and pyroxene reported in petrographic reports from the Instituto de Geología (Chile), along with authigenic chlorite, illite, and calcite recognized by mineralogists associated with the Museo de La Plata. Geochemical fingerprinting uses methods developed at the Corporación Chilena de Innovación (CORFO), comparisons with trace-element signatures from the Andean magmatic arc, and isotopic techniques employed by laboratories at the University of Cambridge and the University of Oxford.
Fossil content includes macrofossils and microfossils documented by teams from the Museo Nacional de Historia Natural (Chile), the Universidad de Chile, and the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), with reported occurrences of marine invertebrates, plant remains, and palynomorph assemblages used for biostratigraphy. Palynological samples linked to research at the British Geological Survey and the Instituto Argentino de Nivología have provided correlations with regional floras known from the Neuquén Group and the Cañadón Asfalto Basin. Fossil studies cite methodological frameworks from the Paleontological Society and comparative collections at the Natural History Museum, London and the American Museum of Natural History.
Sedimentological interpretations by researchers at the Universidad Austral de Chile and the Universidad de Concepción characterize deposition in mixed fluvial to shallow marine settings influenced by contemporaneous activity of the Andean volcanic arc and regional sea-level changes tracked in studies from the International Ocean Discovery Program and the Intergovernmental Oceanographic Commission. Facies analysis draws on models used in the Neuquén Basin and coastal basins of Patagonia to infer progradation, transgression, and volcaniclastic input related to arc volcanism documented by volcanologists at the Geological Society of America and the Society of Economic Paleontologists and Mineralogists (SEPM).
Biostratigraphic and radiometric constraints place the Loncoche interval near the Jurassic–Cretaceous boundary, with correlations to the Tithonian and Berriasian stages used by chronostratigraphers at the International Commission on Stratigraphy and regional stratigraphic committees. Correlative units include the Los Molles Formation and the Vaca Muerta Formation in broader Patagonian schemes, with tie-ins to ammonite zonations and palynomorph assemblages compared against datasets curated by the University of Buenos Aires and the Museo de La Plata.
The volcaniclastic and siliciclastic facies of the formation have been investigated for reservoir potential and aggregate resources by the Comisión Chilena del Cobre, SERNAGEOMIN, and mining companies including Codelco and regional contractors, while local governments such as the Gobierno Regional de la Araucanía have assessed quarrying for construction materials. Geothermal and mineral exploration initiatives reference regional heat-flow studies by the Centro de Estudios en Geotermia and resource assessments by consultants allied with the Inter-American Development Bank and the World Bank for infrastructure planning and sustainable development.
Category:Geologic formations of Chile Category:Geologic formations of Argentina