Sedimentological and provenance response to Cambrian closure of the Clymene ocean: The upper Alto Paraguai Group,Paraguay belt,Brazil |
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| Authors: | José Bandeira Ben McGee Afonso CR Nogueira Alan S Collins Ricardo Trindade |
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| Institution: | 1. Universidade Estadual Paulista (UNESP — IGCE), Programa de Pós-Graduação em Geociências e Meio Ambiente, Av. 24-A, 1515, Rio Claro, SP 13506-900, Brazil;2. Department of Geology and Rubenstein School of the Environment and Natural Resources, University of Vermont, Burlington, VT 05405, USA;3. Universidade Estadual Paulista (UNESP — IGCE), Departamento de Geologia Aplicada, Av. 24-A, 1515, Rio Claro, SP 13506-900, Brazil;4. Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK;5. Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK;6. Universidade Federal de Mato Grosso do Sul — UFMS, Campus do Pantanal, Av. Rio Branco, 1270, Corumbá, MS 79304-020, Brazil;1. Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, Rua do Matão 1226, 05508-090, São Paulo, SP, Brazil;2. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, 100081, China;3. Department of Earth Sciences, Universidad de Concepción, Victor Lamas 1290, Concepción, Chile;4. Departamento de Geofísica and Programa de Pós-Graduação em Geodinâmica e Geofísica, Universidade Federal do Rio Grande do Norte, Natal, 59078-970 RN, Brazil |
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| Abstract: | Final Gondwana amalgamation was marked by the closure of the Neoproterozoic Clymene ocean between the Amazonia craton and central Gondwana. The events which occurred in the last stage of this closure were recorded in the upper Alto Paraguai Group in the foreland of the Paraguay orogen. Outcrop-based facies analysis of the siliciclastic rocks of upper Alto Paraguai Group, composed of the Sepotuba and Diamantino Formations, was carried out in the Diamantino region, within the eastern part of the Barra dos Bugres basin, Mato Grosso state, central-western Brazil. The Sepotuba Formation is composed of sandy shales with planar to wave lamination interbedded with fine-grained sandstone with climbing ripple cross-lamination, planar lamination, swaley cross-stratification and tangential to sigmoidal cross-bedding with mud drapes, related to marine offshore deposits. The lower Diamantino Formation is composed of a monotonous, laterally continuous for hundreds of metres, interbedded siltstone and fine-grained sandstone succession with regular parallel lamination, climbing ripple cross-lamination and ripple-bedding interpreted as distal turbidites. The upper part of this formation consists of fine to medium-grained sandstones with sigmoidal cross-bedding, planar lamination, climbing ripple cross-lamination, symmetrical to asymmetrical and linguoid ripple marks arranged in lobate sand bodies. These facies are interbedded with thick siltstone in coarsening upward large-scale cycles related to a delta system. The Sepotuba Formation characterises the last transgressive deposits of the Paraguay basin representing the final stage of a marine incursion of the Clymene ocean. The progression of orogenesis in the hinterland resulted in the confinement of the Sepotuba sea as a foredeep sub-basin against the edge of the Amazon craton. Turbidites were generated during the deepening of the basin. The successive filling of the basin was associated with progradation of deltaic lobes from the southeast, in a wide lake or a restricted sea that formed after 541 ± 7 Ma. Southeastern to east dominant Neoproterozoic source regions were confirmed by zircon grains that yielded ages around 600 to 540 Ma, that are interpreted to be from granites in the Paraguay orogen. This overall regressive succession recorded in the Alto Paraguai Group represents the filling up of a foredeep basin after the final amalgamation of western Gondwana in the earliest Phanerozoic. |
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