Abstract
Widespread dolomite precipitates, known as cap dolostone, were deposited in the aftermath of the Neoproterozoic Marinoan glaciation, and are thought to reflect dramatic perturbations of seawater chemistry in the aftermath of the glaciation. However, controversy still remains on the nature and the hydrodynamic process of fluids that produced these dolomites. In this study, we present clumped isotope values (Delta (sub 47) ) of Neoproterozoic Marinoan cap carbonates from five sections in Namibia and South China and examine the spatial variation of the post-glacial hydrodynamics across the two carbonate platforms. The Delta (sub 47) -temperatures show the mineral-specific variation in dolostone and limestone, a feature that can be attributed to the solid-state reordering driven by short-term hydrothermal events. Based on the results of theoretical calculations and laboratory experiments, we present a framework that enables the utilization of the reordered clumped isotopes to trace the dolomitization process. Under such a framework, we find the reordering patterns determined by clumped isotopes are indistinguishable from the inner to outer platforms as well as between the dolostone and limestone, which suggests the mixture of meltwater and seawater as the source of dolomitizing fluids. Our findings demonstrate the clumped isotope can be used to trace hydrological processes for deep-time successions, and offer insight into the enigmatic origin of cap carbonates.