Formação ferrífera associada à sedimentação glaciogênica da Formação Puga (Marinoano) na Serra da Bodoquena, MS

No presente artigo descreve-se ocorrencia de formacao ferrifera associada a diamictitos da Formacao Puga (Marionano) em contexto geologico diferente das formacoes ferriferas do Grupo Jacadigo, no Macico de Urucum. A formacao ferrifera ocorre em camada de 2 m de espessura, de direcao NS, com mergulho de 45o E, e encontra-se associada a diamictito de matriz ferruginosa, foliado e com metamorfismo de baixo grau. Apresenta bandamento centimetrico com camadas de hematita e magnetita alternadas com camadas submilimetricas de silica, em parte estiradas devido as deformacoes tectonicas da Faixa Paraguai. Os teores de Fe 2 O 3 variam da ordem de 75%, na base e no topo do pacote, para 52% nas porcoes intermediarias da secao. A concentracao do teor de Fe nas bordas se da pela remobilizacao da silica para o centro do corpo devido, provavelmente, a acao tectonica. Analises quimicas mostram que os teores de Al 2 O 3 sao altos (2,89 - 3,45%) e a forte correlacao com TiO 2 e Zr indicam contribuicao de componentes terrigenos nos sedimentos predominantemente quimicos. Blocos isolados de granito ocorrem na formacao ferrifera, mas a acao tectonica dificulta a observacao das relacoes entre os clastos e o bandamento original. Apesar da Formacao Puga ter sua origem relacionada a eventos glaciogenicos, nao foram encontradas evidencias seguras que permitissem relacionar a origem desta formacao ferrifera a processos glaciais.

[1]  A. Trendall.  The Significance of Iron‐Formation in the Precambrian Stratigraphic Record , 2009 .

[2]  C. Klein.  Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origins , 2005 .

[3]  E. A. Ladeira,et al.  GEOCHEMISTRY AND MINERALOGY OF NEOPROTEROZOIC BANDED IRON-FORMATIONS AND SOME SELECTED, SILICEOUS MANGANESE FORMATIONS FROM THE URUCUM DISTRICT, MATO GROSSO DO SUL, BRAZIL , 2004 .

[4]  B. Kendall,et al.  Constraints on the timing of Marinoan “Snowball Earth” glaciation by 187Re–187Os dating of a Neoproterozoic, post-glacial black shale in Western Canada , 2004 .

[5]  C. Riccomini,et al.  Low‐latitude and multiple geomagnetic reversals in the Neoproterozoic Puga cap carbonate, Amazon craton , 2003 .

[6]  C. Riccomini,et al.  Soft-sediment deformation at the base of the Neoproterozoic Puga cap carbonate (southwestern Amazon craton, Brazil): Confirmation of rapid icehouse to greenhouse transition in snowball Earth , 2003 .

[7]  P. Boggiani,et al.  Integrated correlation of the Vendian to Cambrian Arroyo del Soldado and Corumbá Groups (Uruguay and Brazil): palaeogeographic, palaeoclimatic and palaeobiologic implications , 2003 .

[8]  G. M. Young.  Stratigraphic and tectonic settings of Proterozoic glaciogenic rocks and banded iron-formations: relevance to the snowball Earth debate , 2002 .

[9]  C. D. Alvarenga,et al.  Geological evolution of the Neoproterozoic Corumbágraben system (Brazil). Depositional context of the stratified Fe and Mn ores of the Jacadigo Group , 1998 .

[10]  U. Horstmann,et al.  Chemical composition of banded iron-formations of the Griqualand West Sequence, Northern Cape Province, South Africa, in comparison with other Precambrian iron formations , 1995 .

[11]  N. Beukes,et al.  Sedimentology and geochemistry of the glaciogenic late Proterozoic Rapitan Iron-Formation in Canada , 1993 .

[12]  Joseph L. Kirschvink,et al.  Late Proterozoic low-latitude global glaciation: the snowball Earth , 1992 .

[13]  H. J. Lippolt,et al.  Iron and manganese deposits of the Urucum District, Mato Grosso do Sul, Brazil , 1992 .

[14]  C. D. Alvarenga,et al.  Glacially influenced sedimentation in the Later Proterozoic of the Paraguay belt (Mato Grosso, Brazil) , 1992 .

[15]  G. Gross.  Geochemical Data On Iron - Formations , 1991 .

[16]  N. Beukes,et al.  Geochemistry and sedimentology of a facies transition from limestone to iron-formation deposition in the early Proterozoic Transvaal Supergroup, South Africa , 1989 .

[17]  C. Klein,et al.  Chemistry, petrology and origin of banded iron-formation lithologies from the 3800 MA isua supracrustal belt, West Greenland , 1988 .

[18]  J. H. Breitkopf.  Iron formations related to mafic volcanism and ensialic rifting in the southern margin zone of the Damara Orogen, Namibia , 1988 .

[19]  Julia M. G. Miller.  Glacial and syntectonic sedimentation: The upper Proterozoic Kingston Peak Formation, southern Panamint Range, eastern California , 1985 .

[20]  B. Fryer.  Chapter 8 Part B. Rare Earth Elements in Iron-Formation , 1983 .

[21]  G. M. Young.  The late Proterozoic Tindir Group, east-central Alaska: Evolution of a continental margin , 1982 .

[22]  G. Yeo.  The Late Proterozoic Rapitan Glaciation in the northern Cordillera , 1981 .

[23]  G. M. Young.  Iron-formation and glaciogenic rocks of the Rapitan Group, Northwest Territories, Canada , 1976 .

[24]  N. Beukes.  Precambrian Iron-Formations of Southern Africa , 1973 .

[25]  P. Cloud.  Paleoecological Significance of the Banded Iron-Formation , 1973 .

[26]  J. Dorr.  Manganese and iron deposits of Morro do Urucum, Mato Grosso, Brazil , 1945 .