NEW INSIGHT INTO THE CHARACTER OF THE NEOPROTEROZOIC CARBON CYCLE

Understanding the behavior of the carbon cycle is central to the interpretation of Neoproterozoic geological, climatic and biological events. Despite decades of work on the subject, debate remains regarding the relative sizes of the dissolved inorganic and organic carbon (DIC and DOC) pools and how these relate to the evolution of surface oxidant budgets, namely atmospheric oxygen (pO₂). Here we present >400 new measurements of the carbon isotopic composition of carbonate (δ¹³C_carb) and organic matter (δ¹³C_org), along with total organic carbon contents (TOC), from Neoproterozoic stratigraphic sections in Mongolia, Namibia, and the Yukon. Our data covers over 200 million years of Cryogenian and Ediacaran time and includes three major negative carbon isotope excursions (the Islay, Trezona and Shuram anomalies). These data, interpreted within a stratigraphic context, highlight a number of quantitatively significant relationships between δ¹³C_carb, δ¹³C_org and TOC. Included within these data is extensive evidence for a tight coupling between δ¹³C_carb and δ¹³C_org, as well as provocative relationships between isotopic decoupling and TOC content. Together, these data allow for the re-evaluation of the Neoproterozoic carbon cycle, including the relative sizes of the DIC and DOC pools, and carries implications for climatically relevant atmospheric gasses and surface oxidant budgets.