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| Sierras Bayas Group | |
|---|---|
| Name | Sierras Bayas Group |
| Type | Geologic group |
| Period | Ordovician |
| Age | Early Ordovician to Middle Ordovician |
| Region | Buenos Aires Province, Argentina |
| Country | Argentina |
| Subunits | La Tinta Formation, Loma Negra Formation, Olavarría Formation, Villa Mónica Formation, Sierra Chica de Zárate Formation |
| Overlies | Pampean orogenic belt |
| Underlies | Cañadón Asfalto Formation |
Sierras Bayas Group is an Ordovician stratigraphic succession exposed in central Buenos Aires Province of Argentina, notably around Olavarría and the Sierras Bayas region. The Group records a succession of marine and nearshore deposits that have been crucial for reconstructing Gondwana-margin paleoenvironmental change during the Ordovician radiation and for regional correlations with units in Brazil, Uruguay, and South Africa. It has attracted study by geologists from institutions such as the Universidad Nacional del Centro de la Provincia de Buenos Aires, CONICET, and international teams from University of Buenos Aires, University of Cambridge, and Smithsonian Institution.
The Group crops out around Olavarría and the Sierras Bayas hills within Buenos Aires Province and forms part of the Ordovician successions of the western Gondwana margin that also include units in Sierra de la Ventana, Famatina Range, and the Precordillera. Its stratigraphic framework links to regional tectono-sedimentary belts like the Pampean flat-slab segment and correlates with sequences in San Juan Province and La Pampa Province. Historical mapping by geologists connected to Servicio Geológico Minero Argentino and expeditions organized by Andrés de Castro and Juan Vucetich established baseline lithostratigraphy.
The succession comprises several formations historically subdivided by field teams from Universidad Nacional del La Plata and later refined by researchers affiliated with CONICET and the National Commission on Scientific and Technical Research. Biostratigraphic ties use graptolite and trilobite assemblages comparable to those in the Baltoscandian and Perunica provinces and permit correlation with the Tremadocian to Darriwilian global stages. Regional stratigraphic columns from Olavarría integrate paleomagnetic results produced by groups at University of Buenos Aires and geochemical chemostratigraphy from researchers at University of Córdoba.
Lithologies include siliciclastic sequences of siltstone, shale, sandstone, and carbonate interbeds described by field parties from Universidad Nacional del Centro de la Provincia de Buenos Aires and petrographic studies at Universidad Nacional de La Plata. Depositional models invoke shallow marine shelves, tidal flats, and storm-influenced ramp settings analogous to depositional interpretations applied to the Arenig and Llanvirn successions elsewhere. Sedimentological features such as hummocky cross-stratification and wave-ripple laminae were documented during joint studies by the Argentine Geological Society and teams from University of Buenos Aires.
Fossil assemblages include trilobites, brachiopods, mollusks, graptolites, and ichnofossils collected and cataloged at museums such as the Museo de La Plata, Museo de Ciencias Naturales de Olavarría, and the Museo Argentino de Ciencias Naturales Bernardino Rivadavia. Taxa show affinities with fauna described from Antarctica, South Africa, Brazil, and Uruguay, supporting paleobiogeographic links during Gondwana assembly. Notable paleontologists who contributed to the faunal inventory include researchers from University of Buenos Aires, University of Cambridge, and the Royal Society-affiliated teams that published faunal lists and biostratigraphic zonations.
The Group formed along the passive to active-margin transition of western Gondwana influenced by tectonic events tied to the Famatinian orogeny and far-field stresses related to the Brasiliano orogeny. Paleogeographic reconstructions using data from paleomagnetism laboratories at University of Oxford and Universidad Nacional del La Plata place the succession at mid to high southern latitudes during the Ordovician, with eustatic and tectonic influences compared to those inferred for the Precordillera terrane and the Pampean orogen.
Sedimentary units host industrial minerals and have been investigated for limestones, aggregate, and lithium-hosting clays in broader basins; quarrying around Olavarría supplies building stone and aggregate to regional markets including Buenos Aires. Mineral studies by teams at Servicio Geológico Minero Argentino and INTA evaluated resource potential and environmental impacts; regional exploration campaigns by private firms and public institutions assessed hydrocarbon and metalliferous prospects analogous to evaluations in Santa Cruz Province and Neuquén Basin.
Initial descriptions date to 19th-century geologists associated with Museo de La Plata and later systematic work advanced through 20th-century stratigraphers from Universidad Nacional de La Plata and Universidad Nacional del Sur. Modern studies employ biostratigraphy (trilobites, graptolites) integrated with radiometric ages from authigenic minerals dated using U–Pb zircon techniques at laboratories such as Geoarqueología y Geoquímica Isotópica and chemostratigraphy including carbon isotope curves calibrated against global datasets produced by collaborative networks including International Commission on Stratigraphy contributors. Ongoing work by researchers at CONICET, University of Buenos Aires, and international partners continues to refine chronology and paleoenvironments through multidisciplinary approaches involving sedimentology, paleontology, and isotope geochemistry.
Category:Geology of Argentina Category:Ordovician South America