The nitrogen biogeochemical cycle on Ediacaran rocks: a study on carbonates from the Bambuí Group, São Francisco Basin

Abstract

Nitrogen is an element that conditions life on Earth, and the understanding of how its biogeochemical cycle evolved through geological time provides valuable information about variations of the ocean chemistry, since the speciation of this element is strongly controlled by the redox conditions of the depositional environment. This project aims to obtain N isotopic data (´15N) of carbonates of Ediacaran age, when the biota diversification took place and preceded the Cambrian life explosion. The carbonate successions that will be studied are from the Bambuí Group deposited in the São Francisco basin, in Minas Gerais, Brazil The carbonates of this basin show anomalously high ´13C values interpreted as a result of intense archea methanogenic activity in anoxic environments and methane escape to the atmosphere. The ´15N results will allow to get more information on the water chemistry and on gas exchanges with the atmosphere in the Ediacaran time. Since few fossil occurrences are reported in the Bambuí Group, the results will also help to better understand the ecosystem dynamics at the Ediacaran - Cambrian transition. This work will focus on N isotopic data acquisition and interpretation, and will benefit strongly from the availability of other isotopic data (C, S, Sr) previously obtained on the Bambuí Group, which will allow developing an integrated understanding of the biogeochemistry in this environment. (AU)