Biostratigraphy and paleoenvironmental characterization of the Middle Ordovician from the Sierras Subandinas (NW Argentina) based on organic-walled microfossils and sequence stratigraphy |
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| Authors: | Claudia V Rubinstein Marco Vecoli Ricardo A Astini |
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| Institution: | 1. NEG-LABISE, Department of Geology, Federal University of Pernambuco, P.O. Box 7852, Recife, PE, 50670-000, Brazil;2. Instituto de Geología, Universidad Nacional de San Juan-CONICET, 5400, Argentina;3. Departamento de Paleontologia, Facultad de Ciencias, Iguá, 4225, 11400 Montevideo, Uruguay;4. Instituto Superior de Correlación Geológica (INSUGEO), Miguel Lillo 205, San Miguel de Tucuman 4000, Argentina;5. Institute of Geography and Geology, Geology Section, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark;6. Departamento de Geología, Universidad de Chile, Santiago, Chile;7. Institute of Geosciences, Federal University of Rio Grande do Sul, Porto Alegre, RS, 91509-900, Brazil;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei 430074, China;2. The Department of Land Resource of Shanxi Province, 3 Wangjing Road, Taiyuan, Shanxi 030024, China;3. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, Hubei 430074, China;4. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;5. UMR 8198 Evo-Eco-Paleo, CNRS-Université de Lille, F-59655 Villeneuve d''Ascq, France |
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| Abstract: | Middle Ordovician acritarchs, including enigmatic, spore-like microfossils, are recorded from the Labrado and Capillas formations, of the Sierras Subandinas (Capillas River Section, Sierra de Zapla), northwestern Argentina. The Sierras Subandinas represent the outermost exposures of the Central Andean Basin that display an alternation of shallow-marine deltaic systems and estuarine environments, where relative sea-level fluctuations are frequent. The scarcity of fossils in the section, due to the marginal marine settings and frequent subaerial exposures, hinders the biostratigraphic constraining of these sedimentary successions. Based on the palynological assemblages, a probably Dapingian age is interpreted for the upper Lagunilla Member of the Labrado Formation, whereas the lower part of the Capillas Formation is assigned to the Darriwilian. Acritarchs from the lower part of the Capillas Formation indicate clear affinities with the “peri-Gondwana province”. However the lack of Frankea, a marker taxa for the Middle Ordovician, could be related either to the intermediate paleolatitudinal position of the Central Andean Basin or to local paleoenvironmental conditions. The facies analysis and the distribution of palynomorph assemblages throughout the studied section, suggest that organic-walled microfossils are influenced by local paleoenvironmental conditions. A probable non-marine origin is proposed for the spore-like microfossils co-occurring within the acritarch assemblages. |
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