Micropaleontolgy applied to the stratigraphic and paleoclimatic interpretation of the transition between the Paranoá Group and São Francisco Supergroup (Neoproterozoic, Cabeceiras, Goiás) / Micropaleontologia aplicada na interpretação estratigráfica e paleoclimática da transição entre o Grupo Paranoá e o Supergrupo São Francisco (Neoproterozóico, Cabeceiras, GO)

AUTOR(ES)

Evelyn Aparecida Mecenero Sanchez

DATA DE PUBLICAÇÃO

2010

RESUMO

The Proterozoic record of the Fazenda Funil, near Cabeceiras, GO, includes three sedimentary units: carbonate at the top of Paranoá Group, diamictite of the Jequitaí Formation, and a succession of shale, marl-shale rhythmites, and carbonate of the Sete Lagoas Formation. Microfossiliferous chert occurs in these three units in the form of lenses in the Paranoá Group, clasts within the diamictites of the Jequitaí Formation and as a persistent, 600 meter-long layer in the Sete Lagoas Formation. The similarity of the chert from these three units brings up crucial questions as to the stratigraphy of the Fazenda Funil and the origin of the clasts in the Jequitaí Formation : are they, in fact, of sedimentary (glacial) or tectonic origin? Comparisons among the three units were made of chert fabrics, inorganic aspects (minerals, sedimentary and diagenetic structures), and organic content (microfossils and general characteristics of the organic matter). The analysis of several samples revealed great similarity between the fabrics and microfossils in the three units. Five fabrics and 12 microfossil taxons were identified, two taxons for the first time in the region. These observations led to the conclusion that the chert layer presently attributed to the Sete Lagoas Formation was the source of the chert clasts in the Jequitaí Formation and represents is a slice of the Paranoá Group introduced tectonically within the Bambuí Group during Brasiliano deformation. This layer was eroded and the diamictite deposited presumably during the Sturtian glaciation, even though other evidence of glaciation were not observed on Fazenda Funil. This research, besides clarifying stratigraphic relationships on Fazenda Funil, also demonstrates that Precambrian microfossils can be a very useful tool in research on Proterozoic basins.

ASSUNTO(S)

jequitaí formation proterozoic microfossils formação jequitaí tramas petrográficas microfósseis formação sete lagoas sete lagoas formation proterozoico paranoá group fabrics grupo paranoá

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