A Record of the Snowball Earth Events? The Parecis Basin May Encompass Three Major Neoproterozoic Glaciations on the Amazonian Craton

Abstract

The Parecis Basin is an intracratonic basin located at the south-southeast portion of the Amazonian craton. Its stratigraphic units comprise siliciclastic and carbonate rocks that potentially record intense paleoenvironmental changes related to the Sturtian (∼717–660 Ma), Marinoan (∼657–635 Ma), and Gaskiers (∼580 Ma) glaciations. We present novel X-ray fluorescence geochemistry, C, O and Sr isotopic data from carbonate rock samples retrieved from the stratigraphic well 2ANP 0006 MT. The results show two negative excursions of δ13C here correlated to post-Sturtian and Marinoan glaciations, recorded in the Salto Magessi and Mirassol d’Oeste carbonate units, respectively. Both negative excursions were followed by δ13C positive incursions. At the base of the section, Salto Magessi carbonate presents unradiogenic Sr ratios (87Sr/86Sr from 0.70655 to 0.70776) typical of Cryogenian interglacial carbonate rocks found elsewhere. The negative δ13C excursion from Mirassol d’Oeste is associated with radiogenic 87Sr/86Sr ratios (up to ∼0.7186), possibly related to continental influx from the intense erosion generated by the Marinoan deglaciation. Upward, the Nobres Formation displays preserved primary sulfate minerals (gypsum and anhydrite) and isotopically heavy oxygen compositions which point to an evaporative environment and support the scenario of enhanced oxidative weathering during early to middle Ediacaran. Finally, despite the absence of cap carbonate, diamictites related to the Serra Azul Formation occur overlying the Nobres Formation and are associated with the Gaskiers event. Therefore, the 2ANP 0006 MT may record three major glacial events from the Neoproterozoic, representing a promising section for further studies concerning chemostratigraphic and paleoenvironmental reconstructions during the Neoproterozoic Era.