Artigo Produção Nacional Revisado por pares

Waxing and waning of microbial laminites in the aftermath of the Marinoan glaciation at the margin of the Amazon Craton (Brazil)

2020; Elsevier BV; Volume: 348; Linguagem: Inglês

10.1016/j.precamres.2020.105856

ISSN

1872-7433

Autores

Guilherme Raffaeli Romero, Evelyn Aparecida Mecenero Sanchez, Joelson Lima Soares, Afonso César Rodrigues Nogueira, Thomas R. Fairchild,

Tópico(s)

Geological formations and processes

Resumo

At the margin of the Amazon Craton (west-central Brazil), the Mirassol D'Oeste Formation comprises an emblematic, 16 m-thick Marinoan cap dolostone deposited directly upon diamictites of the Puga Formation. Laterally continuous and morphologically simple microbialites, a common component of Marinoan cap carbonates, begin two meters above the base of the formation and continue upwards as stratiform, domical and irregular wavy microbial laminate boundstones for approximately 10 m. These microbialites consist of alternating thin and thick laminae of peloids (micritized remains of microbial colonies) and subordinate micrite with spar-filled fenestrae that differ in the greater relative abundance of fenestrae in the thicker laminae. The microbialites developed profusely in a calm platformal environment below storm-wave base level, but within the photoic zone, without any contribution of siliciclastics, the Waxing phase of growth. Vertical dolomicrite-filled tubestone structures up to 10 m, occupy the apical portion of the broad domical microbial laminites, Confined percolation of fluids seems the most plausible hypothesis for their origin. The wanning phase began in the final meter of the boundstone consists of irregularly wavy microbial laminites indicating prolonged oscillatory wave-action, followed by dolomitic peloidal grainstone-packstone with megaripple and millimetric macropeloids generated by oscillatory wave action during tradewinds. The hydrodynamic change and a rising sea level put an end to microbialite deposition in the Mirassol D'Oeste cap carbonate.

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