Chemostratigraphic constraints on early Ediacaran carbonate ramp dynamics, Río de la Plata craton, Uruguay

C- and Sr-isotope data for marine carbonates can provide a detailed record of isotopic variations in seawater through time and have proven to be a valuable tool for interpreting biogeochemical events and correlating Neoproterozoic sedimentary successions worldwide. Negative carbon isotope excursion to values as low as − 4.5‰ in the Ediacaran Polanco Limestones Formation, Uruguay has been interpreted as recording the aftermath of a post-Gaskiers glacial event occurred elsewhere on southwest Gondwana. The record of both deep- and shallow-water settings in the Polanco Limestone Formation provides an opportunity to examine δ13C variability across the platform and to evaluate whether the carbon isotope values reflect local or global processes. Herein we provide high-resolution δ13C-chemostratigraphy and Sr-isotope data from stratigraphic sections comprising proximal and distal settings on the carbonate platform. Carbon isotopic values are negative in deep-water facies but progressively rise towards positive values in shallow-water settings. This previously unrecognized trend suggests that deposition of Polanco carbonates occurred in a stratified marine basin where degradation of organic matter below the redox boundary led to lower δ13C values at greater depths. The negative δ13C excursion is restricted to specific horizons in shallow-water facies and is interpreted as being originated due to higher levels of reworking under storm-dominated conditions, which produced a strong local oxidation of organic matter and ultimately, the negative carbon isotope signatures. 87Sr/86Sr and δ13C chemostratigraphy coupled with new radiometric data allow us to revise the previously proposed age for the unit. This new data support an age between 590 and 560 Ma for the deposition of the Polanco Limestones Formation.

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► C-, O-, and Sr-isotope composition of early Ediacaran carbonates
► δ13C variability across the carbonate platform
► Stratified marine basin
► Organic matter remineralization under storm-dominated conditions