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| Los Molles Formation | |
|---|---|
| Name | Los Molles Formation |
| Type | Geological formation |
| Period | Jurassic |
| Age | Early to Middle Jurassic |
| Namedfor | Los Molles |
| Region | Neuquén Basin, Mendoza Province |
| Country | Argentina |
Los Molles Formation
Los Molles Formation is an Early to Middle Jurassic marine sedimentary unit exposed in the Neuquén Basin of western Argentina. The formation is significant for its organic-rich mudstones, fossil assemblages, and importance to regional hydrocarbon exploration, intersecting research by institutions such as the Servicio Geológico Minero Argentino, the Yacimientos Petrolíferos Fiscales, and international teams from the University of Buenos Aires and the Universidad Nacional del Comahue. Its study connects to broader Jurassic research involving the Patagonia region, the Andes Mountains orogeny, and conjugate margin comparisons with the South Atlantic Ocean opening.
Los Molles Formation occupies a stratigraphic position within the Neuquén Basin, a back-arc basin influenced by Mesozoic tectonics associated with the subduction of the Nazca Plate beneath western South America and the subsequent evolution of the Andean orogeny. The unit overlies synrift and early postrift sequences and is laterally adjacent to volcanic and sedimentary units correlated with the Toarcian and Aalenian stages represented elsewhere in Gondwana. Regional mapping by the Dirección Nacional del Servicio Geológico and basin studies by operators such as YPF and multinational companies link Los Molles to broader petroleum systems documented across the Neuquén Province, Mendoza Province, and onto the Río Negro Province margins.
Stratigraphically, Los Molles is part of a Jurassic succession that includes the underlying synrift units related to the Cuyo Basin rifting and the overlying units such as the Vaca Muerta Formation in some stratigraphic frameworks. Biostratigraphic control derives from ammonite assemblages comparable to those in the Andean Basin and radiometric tie-points provided by interbedded volcanic ashes correlated to regional ash beds described in the Geological Time Scale literature. Regional correlation employs sequence stratigraphy techniques used by industry consortia including the Sociedad Geológica de España-affiliated groups and South American stratigraphers connecting Los Molles with coeval units in the Falkland Islands and southwestern Africa.
Lithologically, Los Molles is dominated by dark, organic-rich siliceous and calcareous mudstones, black shales, and chert-rich horizons, with subordinate siltstones and fine sandstones. Petrographic and geochemical investigations by teams from the National University of La Plata and the Instituto de Estudios Andinos document high total organic carbon (TOC) contents, lamination indicative of low-oxygen bottom waters, and diagenetic pyrite associated with euxinic conditions similar to models applied in studies by the Istituto Nazionale di Geofisica e Vulcanologia and the British Geological Survey. Sedimentological features include thin-bedded turbidites, hemipelagic deposits, and distal facies transitions comparable to other Jurassic black shale systems studied in the North Sea and the Western Interior Seaway.
Los Molles preserves marine fossils including ammonites, belemnites, bivalves, marine vertebrates, and microfossils such as foraminifera and radiolarians. Paleontological work by researchers associated with the Museo Argentino de Ciencias Naturales and the Museo de La Plata has yielded taxa useful for biostratigraphy and paleoecology, with faunal affinities to assemblages documented in the Moroccan and European Jurassic basins. Vertebrate remains, including ichthyosaurs and plesiosaurs reported in Neuquén Basin localities, link paleobiological research to global marine reptile studies by institutions like the Natural History Museum, London and the Smithsonian Institution.
Interpretations of depositional environment indicate a deepening marine basin with restricted circulation and periodic anoxia, forming an oxygen-depleted seafloor favorable to organic matter preservation. Paleoenvironmental reconstructions align Los Molles with transgressive systems tracts and condensed sections recognized in Jurassic global events such as the Toarcian Oceanic Anoxic Event, drawing comparisons to black shale deposits studied in the Boreal Realm and the Tethys Ocean. Paleogeographic models situate the Neuquén Basin along the southwestern margin of Gondwana, with plate reconstructions by groups at the Paleomap Project and the University of Texas Institute for Geophysics providing context for regional oceanographic circulation patterns.
Los Molles is a key source and unconventional reservoir interval within the Neuquén Basin petroleum system exploited by national and international energy companies including YPF, Pan American Energy, and multinational consortia. High TOC and thermally mature intervals make it a targeted unit for shale gas and shale oil exploration and production, with appraisal campaigns employing horizontal drilling and hydraulic fracturing technologies developed by service firms such as Schlumberger and Halliburton. Reservoir characterization efforts involving the Society of Petroleum Engineers-affiliated studies and basin modeling by the International Energy Agency emphasize its role in Argentina's hydrocarbon strategy and resource assessments conducted by the US Energy Information Administration and the Organization of the Petroleum Exporting Countries comparisons.
Scientific investigation of Los Molles began with early 20th-century mapping by Argentine geologists associated with the Comisión de Estudios Geológicos and intensified during mid-20th-century petroleum exploration by YPF and international partners. Modern multidisciplinary studies incorporate biostratigraphy, chemostratigraphy, carbon isotope stratigraphy, and radiometric dating (U-Pb zircon ages from intercalated tuffs) produced by laboratories at the University of Toronto and the Max Planck Institute for Chemistry, constraining Los Molles to Early-to-Middle Jurassic intervals. Ongoing research collaborations among the Universidad Nacional de La Plata, the Universidad Nacional del Comahue, and industry continue to refine depositional models, sequence stratigraphy, and resource estimates relevant to both Argentine geology and global Jurassic stratigraphic correlation.
Category:Geologic formations of Argentina Category:Jurassic System of South America Category:Neuquén Basin