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| 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 |
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| 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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| 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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