Sulfur and Carbon biogeochemical cycles in the Ediacaran and their record in Brazilian sedimentary successions

Abstract

The most remarkable changes in the Earth's life evolution took place during the Ediacaran Period, when the first macroscopic complex organisms emerged. Geochemical proxies show major fluctuations coupled to the paleontological record appearances, which point to the evolution of the whole ocean-atmosphere-biosphere system. The main event considered as the trigger for this turning point is the final oxygenation of the oceans and atmosphere. Regarding the sulphur, great ´34S excursions in the marine sulphate through Neoproterozoic record would be resulted of a smaller reservoir when compared to the modern values, reaching these levels only at the Ediacaran Period. These excursions are coupled to the ´13C record, as the rise of atmospheric oxygen and marine sulphate levels led to changes in the organic carbon cycle. Despite these recognized anomalies, there is no agreement concerning the biogeochemical processes involved, besides the need for data from West Gondwana to the global record. The main goal of this project is to access Brazilian Ediacaran sections (South Paraguay Belt and São Francisco Basin) to provide C (carbonate and organic matter) and S (sulphate and sulphide) isotope chemostratigraphic data supported by detailed microfaciological study. The results will improve the stratigraphic resolution of Ediacaran record in the Brazilian deposits, as well as to contribute to the understanding of the C and S isotopic global record. Additionally, more detailed paleoenvironmental inferences concerning the events in this period will be possible. Therefore, it will improve the comprehension of biogeochemical cycles at the end of Neoproterozoic Era and the key events that led to the rise of complex organisms in the Earth.