Phosphatic strata from Ponta Grossa Formation in Rio Verde de Mato Grosso, Mato Grosso do Sul, Brazil: palaeoenvironmental implications

Authors

  • Cibele Carolina Montibeller Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP, Instituto de Geociências e Ciências Exatas, Pós-Graduação em Geociências e Meio Ambiente.
  • Antenor Zanardo Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP, Instituto de Geociências e Ciências Exatas, Departamento de Petrologia e Metalogenia.
  • Guillermo Rafael Beltran Navarro Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP, Instituto de Geociências e Ciências Exatas, Departamento de Petrologia e Metalogenia.

DOI:

https://doi.org/10.11606/issn.2316-9095.v18-396

Keywords:

Phosphorite, Phosphogenesis, Devonian, Paraná Basin, Ponta Grossa Formation.

Abstract

Amongst rocks of the Ponta Grossa Formation cropping out in Rio Verde de Mato Grosso, there are levels consisting predominantly of apatite, without fossil traces, which occur as layers hosted in gray to black shales. Petrographically, this phosphatic level has subtly layered structure and no features indicative of algae, fossil remains or organic structures. It has P2O5 content varying between 12.96 and 23.35%, CaO ranging between 19.85 and 33.04%, and high concentration of rare earth elements (REE) when compared to the average content of the upper continental crust. This occurrence exhibits no evidence of biogenic action, which is confirmed by electron microscopy, yet it  contains relicts of oxy-hydroxides, predominantly of iron, with small amount of manganese, suggesting origin from phosphate desorption due to the redox behavior of these oxy-hydroxides. If these phosphorites were not subject to external supply of iron oxy-hydroxides due to proximity to the coast, deltaic environments or hydrothermal and/or volcanic contributions, then the phosphatic levels of Rio Verde de Mato Grosso, Mato Grosso do Sul, probably formed on a shallow marine platform at depths between 200 and 300 m, in cold, low salinity and preferably anoxic water, subject to upwelling.

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Published

2018-03-01

Issue

Vol. 18 No. 1 (2018)

Section

Articles

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How to Cite

Montibeller, C. C., Zanardo, A., & Navarro, G. R. B. (2018). Phosphatic strata from Ponta Grossa Formation in Rio Verde de Mato Grosso, Mato Grosso do Sul, Brazil: palaeoenvironmental implications. Geologia USP. Série Científica, 18(1), 241-257. https://doi.org/10.11606/issn.2316-9095.v18-396