Environmental change at the end of the Snowball Earth and implications for the emergence of the first animals

The Neoproterozoic era (1000-540 Ma) contains sufficient evidence to propose large-scale glacial events and the emergence of the first animals. The Snowball Earth includes two main glacial events, the Sturtian (~720Ma) and the Marinoan (~635Ma). Cap carbonates deposited at the termination of the Marinoan glaciation are hypothesised to be archives for seawater composition and understanding environmental change at the end of the Neoproterozoic. The aftermath of the Marinoan glaciation is characterised by rapid deglaciation which is thought to have exposed glacial rock powder, promoting a pulse in silicate weathering. This pulse of weathering is suggested to have provided an influx of nutrients to the ocean possibly triggering evolution of early life, leading to the emergence of Ediacara biota. The objectives of this project are to investigate the environmental changes at the end of the Marinoan glaciation and the subsequent implications for the emergence of early life. To achieve this, lithium (Li) isotopes are used from cap carbonates of the Nuccaleena Formation in South Australia. Lithium isotopes in carbonates can be used as a proxy for riverine fluxes to the oceans, reflecting conditions of continental weathering. As these cap carbonates contain various amounts of detrital material, a leaching protocol is used to extract Li from the carbonate fraction only. The analysis of mineral abundances, major and trace elements and Li isotopes has provided evidence to suggest that low δ7 Li values recorded at the onset of deglaciation represent high weathering intensities. During this period of high weathering intensity, it is suggested through mineralogical analysis that there was an increased flux in clastic sediment, causing an increase in silicate mineral abundance at the onset of deglaciation. These high weathering conditions are suggested to have caused an impulse of elements into the oceans possibly triggering the evolution of the Ediacaran organisms.