Temporal evolution of shallow marine diagenetic environments: Insights from carbonate concretions

Early diagenesis of marine organic matter dramatically impacts Earth’s surface chemistry by changing the burial potential carbon and promoting formation authigenic mineral phases including carbonate concretions. Marine sediment-hosted concretions tend to form as a result microbial anaerobic diagenetic reactions that degrade methane, some which require an external oxidant. Thus, temporal changes in oxidation state oceans may impart first-order control on concretion authigenesis mechanisms through time. Statistically significant variability isotope compositions indicates shallow sediment associated with evolving redox landscape. This manifests itself expansion composition range broadly characterized increase maximum decrease minimum values Reaction transport modelling helps constrain shifting highlights importance delivery seafloor, sulfate concentrations, methane production influx. The first appearance conclusively methane-derived occurs Carboniferous coincides Paleozoic rise sulfate. muted recognized older (and particular for Precambrian concretions) likely reflects smaller reservoir perhaps elevated dissolved inorganic concentrations. Causes time are more confounding, but be related isotopic equilibration externally derived methane. Ultimately record part availability state, highlighting connections subsurface biosphere throughout geologic