Fingerprinting local controls on the Neoproterozoic carbon cycle with the isotopic record of Cryogenian carbonates in the Panamint Range, California

Abstract Neoproterozoic carbon isotope excursions are commonly attributed to changes in the global fraction of organic carbon burial associated with climate instability and/or oxygenation. Here we show that carbonate sediment deposited during the ca. 661 – δ 13 Ccarb values of ∼+4 to +9‰, whereas values of stratigraphically equivalent dolostones are consistently lower, between ∼-4 and +4‰. Field observations and analyses of clasts from the overlying Marinoan glacial diamictite show that the offset in δ 13 Ccarb values resulted from pre- to syn-Marinoan dolomitization. Further, δ 44 / 40 Ca and δ 26 Mg data indicate that this isotopic variability resulted from sediment-buffered diagenesis. We propose that extremely positive δ 13 Ccarb values record local primary productivity within restricted platform surface waters and/or oxygenated pore fluids and negative values reflect anaerobic remineralization of organic carbon within sediment pore waters. In this scenario, neither the original calcite/aragonite nor subsequent dolomite precipitates of the Thorndike submember record δ 13 Ccarb values that are representative of global Cryogenian seawater, and instead they archive the evolution of local dissolved inorganic carbon pools.