Carbon and oxygen isotope geochemistry of Ediacaran outer platform carbonates, Paraguay Belt, central Brazil

Abstract

After the late Cryogenian glaciation the central region of Brazil was the site of extensive deposition of platformal carbonates of the Araras Group. This group includes a basal cap carbonate sequence succeeded by transgressive, deep platform deposits of bituminous lime mudstone and shale. Facies and stratigraphic data combined with carbon and oxygen isotopic analyses of the most complete section of the transgressive deposits, exposed in the Guia syncline, were used to evaluate the depositional paleoenvironment and to test the correlation of these deposits along the belt and with other units worldwide. The studied succession consists of 150 m thick tabular beds of black to grey lime mudstone and shale with predominantly negative δ 13 C PDB values around -2.5 to −1 • / •• . The δ 13 C PDB profile of Guia syncline shows a clear correlation with the upper portion of Guia Formation in the Cáceres region, about 200 km to the southwest. The δ 13 C PDB profile of the Araras Group is comparable with δ 13 C PDB profiles of Ediacaran units of the southern Paraguay Belt, western Canada, and the Congo and Kalahari cratons. Moreover, facies distribution, stratigraphy and the carbon isotopic profile of the Araras Group match the middle Tsumeb Subgroup in Namibia, which reinforces the Ediacaran age assigned to the Araras Group.

Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil

“…The first sector was developed during the Brasiliano Cycle [8,9], and the stratigraphy mainly consists of metaepiclastites and low-grade metasedimentary units of the Cuiabá Group (850-630 Ma). The lower unit contains metalimestones of the Araras Group (approximately 580 Ma); the upper unit includes low-grade metasedimentary formations of the Alto Paraguay Group (590-545 Ma) [10][11][12].…”

Correlations of some Neoproterozoic carbonate-dominated successions in South America based on high-resolution chemostratigraphy

“…The cap dolostone of the Mirassol d'Oeste Formation is succeeded by transgressive, deep-platformal deposits of dark gray laminated lime-mudstone and shale of the Guia Formation, reaching up to 250 m thick in the middle shelf domain Riccomini et al 2007;Alvarenga et al 2004Alvarenga et al , 2008Alvarenga et al , 2011. These trangressive deposits are exposed along more than 200 km from West to East (Alvarenga et al 2008.…”

Caracterização tafonômica e estratigráfica de Cloudina lucianoi (Beurlen & Sommer, 1957) Zaine & Faircild, 1985, no Grupo Corumbá, ediacarano do sudeste do Brasil

“…O hábito gregário deste organismo , junto com sua freqüente associação em grandes acumulações com estromatólitos e trombólitos, ou mesmo preservado em posição vertical ou sub-horizontal dentro de trombólitos, apoiam esta concepção, que também é reforçada pela presença de outros metazoários de morfologia compatível a um estilo de vida séssil, como Namacalathus e Namapoikia, no mesmo contexto deposicional Horfmann & Mountjoy 2001;Wood et al 2002;Wood 2011). Estas observações sugerem uma comunidade composta por metazoários filtradores ou microcarnívoros, oportunistas, cujo hábito gregário favoreceria estes organismos na competição por espaço, e também na estabilização do substrato (Jackson 1983;Wood 2011 (Babinski et al 2006Nogueira et al 2007;Riccomini et al 2007), sendo que a ocorrência de metazoários é limitada ao último grupo Boggiani et al 2010). (Almeida 1965;Del'Arco et al 1981;Boggiani 1998;Gaucher et al 2003;Oliveira 2010 Esta formação é a mais fossilífera do Grupo Corumbá, e reveste-se de grande importância por conter os mais antigos metazoários no registro paleontológico brasileiro: Cloudina lucianoi e Corumbella werneri Walde et al 1982;Zaine e Fairchild 1985;Gaucher et al 2003).…”