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

• C, O, Ca, and Mg isotope data from Cryogenian carbonates in Death Valley, CA (USA). • Consistent with sediment-buffered aragonite deposition for Sturtian cap carbonate. • Early-burial dolomitization lowered δ 13 C of Cryogenian carbonates by up to 10‰. • δ 13 C values reflect isotopic compositions of local, rather than global, reservoirs. • Remineralization of platform and pore fluid organic carbon may have played a role. 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 – <651 Ma Cryogenian non-glacial interlude between the Sturtian and Marinoan glaciations exhibit lateral offsets in carbonate-carbon isotope values from coeval units by as much as 10‰. Within the Thorndike submember of the Cryogenian succession in the Panamint Range, California, USA, carbonate-carbon isotope values can be linked to a laterally discontinuous dolomitization front: limestones exhibit δ 13 C carb 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 C carb 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 C carb 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 C carb values that are representative of global Cryogenian seawater, and instead they archive the evolution of local dissolved inorganic carbon pools. [ABSTRACT FROM AUTHOR]