Triple oxygen isotope measurements in chert: insights into the Snowball Earth glaciations

Abstract

Snowball Earth events represent a critical component of the history of the planet, particularly for the trajectory of life, atmospheric oxygen, and planetary habitability. There remains a myriad of questions about the dynamics of these global glaciations, especially regarding the relationship between the cryosphere and hydrosphere during this time. This study analyzes silica precipitates within a carbonate sequence immediately underlying a Cryogenian diamictite to better understand this relationship, particularly the chemistry of subglacial meltwater. Using triple oxygen isotope measurements, clumped isotope palaeothermometry, uranium-lead geochronology, and SEM/EDS and XRD analyses, we present interpretations of both the host rock and possible scenarios for the geochemistry of the precipitating fluid(s) responsible for these silica cements. We posit that these cherts are precipitates either from syn-glacial, sub-ice meltwaters or deglacial fluids from the end of the Marinoan glaciation, providing useful insights into the chemical composition of these source waters and demonstrating the utility of chemical precipitates as a record of ancient sub-ice conditions.