Carbon isotope fluctuations in precambrian carbonate sequences of several localities in Brazil
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| Natura: | Artículo científico |
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Academia Brasileira de Ciências
2000
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| _version_ | 1876467879001456640 |
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| author | Alcides N. Sial |
| author_facet | Alcides N. Sial |
| contents | Carbon isotope fluctuations in precambrian carbonate sequences of several localities in Brazil Alcides N. Sial Valderez P. Ferreira Afonso R. Dealmeida Antonio W. Romano Clovis V. Parente Marcondes L. da Costa Victor H. Santos Multidisciplinaria (Ciencias Naturales y Exactas) Archean carbonates Neoproterozoic carbon isotopes Paleoproterozoic Carbon isotope fluctuations in Precambrian sedimentary carbonates between 2.8 Ga and 0.60 Ga in Brazil are examined in this study. The carbonate facies of the BIF of the 2.8 Ga-old Carajás Formation, state of Pará in northern Brazil, has rather homogeneous d13C (-5 o/ooPDB), compatible with carbonatization of a silicate protolith by a CO2-rich fluid from mantle degassing. The Paleoproterozoic Gandarela Formation, state of Minas Gerais, displays a narrow d13C variation (-1.5 to +0.5 o/oo) compatible with carbon isotope signatures of carbonates deposited around 2.4 Ga worldwide. The Fecho do Funil Formation has probably recorded the Lomagundi d13C positive anomaly (+6.4 to +7.1 o/ooPDB). The magnesite-bearing carbonates of the Orós mobile belt, state of Ceará, exhibit carbon isotope fluctuation within the range for carbonates deposited at 1.8 Ga. The C-isotope record of the Frecheirinha Formation, northwestern state of Ceará, shows negative d13C values in its lower portion (-2 o/oo) and positive values up section (+1 to +3 o/oo), which suggests this sequence is a cap carbonate deposited after a glacial event around 0.95 Ga. The Jacoca and Acauã sedimentary carbonate Formations, state of Sergipe, NE Brazil, show carbon isotope fluctuations very similar to each other (average around -5 o/oo), compatible with a deposition around 0.76 Ga. The younger Olho D´Água carbonate Formation, however, also in the state of Sergipe, displays negative d13C values at the lower portion of the Formation, changing dramatically up section to positive values as high as +10 o/oo, a characteristic compatible with a Sturtian cap carbonate deposited around 0.69 Ga. On the light of the C isotope data discussed in this study, it seems that d13C fluctuations in Paleoproterozoic carbonates in Brazil are within the range found globally for metasedimentary carbonates of this age. Carbon isotope data proved to be very useful in establishing relative chronology of Neoproterozoic carbonate formations for which precise radiometric ages are not available. 2000 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32772406 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.4 Vol.72 |
| format | Artículo científico |
| id | redalyc_32772406 |
| institution | Redalyc |
| language | en |
| publishDate | 2000 |
| publisher | Academia Brasileira de Ciências |
| spellingShingle | Carbon isotope fluctuations in precambrian carbonate sequences of several localities in Brazil Alcides N. Sial Multidisciplinaria (Ciencias Naturales y Exactas) Archean carbonates Neoproterozoic carbon isotopes Paleoproterozoic Carbon isotope fluctuations in precambrian carbonate sequences of several localities in Brazil Alcides N. Sial Valderez P. Ferreira Afonso R. Dealmeida Antonio W. Romano Clovis V. Parente Marcondes L. da Costa Victor H. Santos Multidisciplinaria (Ciencias Naturales y Exactas) Archean carbonates Neoproterozoic carbon isotopes Paleoproterozoic Carbon isotope fluctuations in Precambrian sedimentary carbonates between 2.8 Ga and 0.60 Ga in Brazil are examined in this study. The carbonate facies of the BIF of the 2.8 Ga-old Carajás Formation, state of Pará in northern Brazil, has rather homogeneous d13C (-5 o/ooPDB), compatible with carbonatization of a silicate protolith by a CO2-rich fluid from mantle degassing. The Paleoproterozoic Gandarela Formation, state of Minas Gerais, displays a narrow d13C variation (-1.5 to +0.5 o/oo) compatible with carbon isotope signatures of carbonates deposited around 2.4 Ga worldwide. The Fecho do Funil Formation has probably recorded the Lomagundi d13C positive anomaly (+6.4 to +7.1 o/ooPDB). The magnesite-bearing carbonates of the Orós mobile belt, state of Ceará, exhibit carbon isotope fluctuation within the range for carbonates deposited at 1.8 Ga. The C-isotope record of the Frecheirinha Formation, northwestern state of Ceará, shows negative d13C values in its lower portion (-2 o/oo) and positive values up section (+1 to +3 o/oo), which suggests this sequence is a cap carbonate deposited after a glacial event around 0.95 Ga. The Jacoca and Acauã sedimentary carbonate Formations, state of Sergipe, NE Brazil, show carbon isotope fluctuations very similar to each other (average around -5 o/oo), compatible with a deposition around 0.76 Ga. The younger Olho D´Água carbonate Formation, however, also in the state of Sergipe, displays negative d13C values at the lower portion of the Formation, changing dramatically up section to positive values as high as +10 o/oo, a characteristic compatible with a Sturtian cap carbonate deposited around 0.69 Ga. On the light of the C isotope data discussed in this study, it seems that d13C fluctuations in Paleoproterozoic carbonates in Brazil are within the range found globally for metasedimentary carbonates of this age. Carbon isotope data proved to be very useful in establishing relative chronology of Neoproterozoic carbonate formations for which precise radiometric ages are not available. 2000 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32772406 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.4 Vol.72 |
| title | Carbon isotope fluctuations in precambrian carbonate sequences of several localities in Brazil |
| topic | Multidisciplinaria (Ciencias Naturales y Exactas) Archean carbonates Neoproterozoic carbon isotopes Paleoproterozoic |
| url | https://www.redalyc.org/articulo.oa?id=32772406 |