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Registros recuperados: 7
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Acritarchs of the Ediacaran Frecheirinha Formation, Ubajara Group, Northeastern Brazil Anais da ABC (AABC)
Chiglino,Leticia; Gaucher,Claudio; Sial,Alcides N.; Ferreira,Valderez P..
We report for the first time the occurrence of organic-walled microfossils in Ediacaran limestones and marls of the Frecheirinha Formation, Ubajara Group, and the first Precambrian acritarchs so far reported for northeastern Brazil. The assemblage of the Frecheirinha Formation represents a low-diversity microflora comprising Leiosphaeridia, Lophosphaeridium and subordinated Bavlinella (=Sphaerocongregus). Their thermal alteration index (TAI) between 4+ and 5, suggests metamorphic temperatures exceeding 200-250°C. Higher temperatures are probably related to intruding granitic plutons (Meruoca, Mucambo). Reported δ13C values of carbonates of -3.5 ‰ VPDB (Vienna-Peedee Belemnite) at the base, passing up section into a positive plateau of up to +3.7 ‰, and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Acritarchs; Ediacaran; Neoproterozoic; Northeastern Brazil.
Ano: 2015 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000200635
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C- and Sr-isotope stratigraphy of the São Caetano complex, Northeastern Brazil: a contribution to the study of the Meso-Neoproterozoic seawater geochemistry Anais da ABC (AABC)
Silva,Juan C.; Sial,Alcides N.; Ferreira,Valderez P.; Pimentel,Márcio M..
C-isotope and 87Sr/86Sr values for five carbonate successions from the São Caetano Complex, northeastern Brazil, were used to constrain their depositional age and to determine large variations in the C- and Sr-isotopic composition of seawater under the framework of global tectonic events. Three C-isotope stages were identified from base to top in a composed chemostratigraphic section: (1) stage in which delta13C values vary from +2 to +3.7‰ PDB and average 3‰ PDB, (2) stage with delta13C values displaying stronger oscillations (from -2‰ to +‰ PDB), and (3) stage with an isotopic plateau with values around +3.7‰ PDB. Constant 87Sr/86Sr values (~ 0.70600) characterize C-isotope stage 1, whereas slightly fluctuating values (from 0.70600 to 0.70700)...
Tipo: Info:eu-repo/semantics/article Palavras-chave: C-isotopes; Meso-Neoproterozoic; Chemostratigraphy; Borborema Province; Northeastern Brazil.
Ano: 2005 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000100011
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Carbon and oxygen isotope geochemistry of Ediacaran outer platform carbonates, Paraguay Belt, central Brazil Anais da ABC (AABC)
Riccomini,Claudio; Nogueira,Afonso C.R.; Sial,Alcides N..
After the late Cryogenian glaciation the central region of Brazil was the site of extensive deposition of platformal carbonates of the Araras Group. This group includes a basal cap carbonate sequence succeeded by transgressive, deep platform deposits of bituminous lime mudstone and shale. Facies and stratigraphic data combined with carbon and oxygen isotopic analyses of the most complete section of the transgressive deposits, exposed in the Guia syncline, were used to evaluate the depositional paleoenvironment and to test the correlation of these deposits along the belt and with other units worldwide. The studied succession consists of 150 m thick tabular beds of black to grey lime mudstone and shale with predominantly negative delta13C PDB values around...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Carbon and oxygen isotopes; Ediacaran; Araras Group; Guia Formation; Amazon Craton; Glaciation.
Ano: 2007 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000300012
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Carbon isotopes and the K-T boundary in Argentina and Chile Anais da ABC (AABC)
Ferreira,Valderez P.; Sial,Alcides N.; Parada,Miguel A.; Toselli,Alejandro J.; Aceñolaza,Florencio G..
Tipo: Info:eu-repo/semantics/article
Ano: 2000 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652000000400023
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Carbonate cements in contemporaneous beachrocks, Jaguaribe beach, Itamaracá island, northeastern Brazil: petrographic, geochemical and isotopic aspects Anais da ABC (AABC)
Guerra,Núbia C.; Kiang,Chang H.; Sial,Alcides N..
Holocene beachrocks of the Jaguaribe beach, State of Pernambuco, northeastern Brazil, consist of horizontal, cemented layers approximately 40 cm thick. The cement shows three textural varieties: (a) calciferous, surrounding siliciclastic grains, (b) micritic, with an acicular fringe; and (c) cryptocrystalline calcite in pores. Early cementation took place at the water table below beach ridges, where geochemical, hydrodynamic and, perhaps, also microbiological conditions favored rapid precipitation of aragonite and/or high-Mg calcite. delta13C values range from -1.8 to +1.5‰ for dissolved carbonate in interstitial water and from +0.2 to +2.1‰ for bioclastic components. delta18O values range from -2.8 to +0.5‰ for seawater, freshwater and interstitial water....
Tipo: Info:eu-repo/semantics/article Palavras-chave: Beachrocks; Early diagenesis; O and C isotopes; Holocene.
Ano: 2005 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000200011
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delta13C fluctuations in precambrian to cambrian carbonate sequences in NE Brazil and NW Argentina Anais da ABC (AABC)
Sial,Alcides N.; Ferreira,Valderez P.; Toselli,Alejandro J.; Aceñolaza,Florencio G.; Alonso,Ricardo; Parada,Miguel A..
Tipo: Info:eu-repo/semantics/article
Ano: 2000 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652000000400022
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Oceanographic parameters in continental margin of the State of Ceará (northeastern Brazil) deduced from C and O isotopes in foraminifers Anais da ABC (AABC)
Marques,Wanessa S.; Menor,Eldemar de A.; Sial,Alcides N.; Manso,Valdir A.V.; Freire,Satander S..
Specimens of Recent foraminifera of Amphistegina radiata, Peneroplis planatus and Globigerinoides ruber, from fifty samples of surface sediments of the continental margin of the State of Ceará, Brazil, have been analyzed for carbon and oxygen isotopes to investigate oceanographic parameters and determine the values of delta18O of the oceanic water. From a comparison between values of delta18O obtained for ocean water using the linear equations by (Craig and Gordon 1965) and the one by Wolff et al. (1998), it became evident that the former yielded a more reliable value (0.2‰ SMOW) than the latter. Lower values of delta18O for the ocean water in this continental margin resulted from continental water influence. Values of 18O (-0.3‰ to -1.5‰ PDB for benthic...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Foraminifers; Carbon and oxygen isotopes; Continental margin; Ceará; Brazil.
Ano: 2007 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000100015
Registros recuperados: 7
Primeira ... 1 ... Última
 

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