Interlinked marine cycles of methane, manganese, and sulfate in the post-Marinoan Doushantuo cap dolostone

Oceanic Redox State During the Early Cambrian: Insights From Mo‐S Isotopes and Geochemistry of Himalayan Shales

“…The δ 34 S data for pyrites and carbonate‐associated sulfur (CAS) have also documented a dynamic seawater sulfate reservoir with variable sulfate concentrations (<2–10 mM) across the Pc‐C transition (Algeo et al., 2015; Feng et al., 2014; Jin et al., 2016; Li et al., 2023; Loyd et al., 2012). These studies also show an appreciable impact of anaerobic oxidation of methane in sedimentary sequences in South China regulated by sulfate inventory (Cai et al., 2023; Peng et al., 2022). The Ediacaran‐Cambrian sections from China (Li et al., 2009), Oman (Amthor et al., 2003), Mongolia (Brasier et al., 1996), Namibia (Grotzinger et al., 1995), and India (Aharon et al., 1987; Banerjee et al., 1997) document a global negative δ 13 C excursion (magnitude 5–10‰) in carbonates, signifying a change in carbon cycling and seawater chemistry during the interval.…”

“…Sulfur isotopic studies in Ediacaran sections indicate significant fluctuation in the oceanic sulfate concentrations mainly linked to glaciation and subsequent changes in continental influxes (Peng et al., 2022). The sulfate content during the Ediacaran, barring glaciation‐related variability, was significantly lower (Algeo et al., 2015; Cai et al., 2015, 2023) than the modern‐day value (∼28 mM). The δ 34 S data for pyrites and carbonate‐associated sulfur (CAS) have also documented a dynamic seawater sulfate reservoir with variable sulfate concentrations (<2–10 mM) across the Pc‐C transition (Algeo et al., 2015; Feng et al., 2014; Jin et al., 2016; Li et al., 2023; Loyd et al., 2012).…”

“…an appreciable impact of anaerobic oxidation of methane in sedimentary sequences in South China regulated by sulfate inventory (Cai et al, 2023;Peng et al, 2022). The Ediacaran-Cambrian sections from China (Li et al, 2009), Oman (Amthor et al, 2003), Mongolia (Brasier et al, 1996), Namibia (Grotzinger et al, 1995), and India (Aharon et al, 1987;Banerjee et al, 1997) document a global negative δ 13 C excursion (magnitude 5-10‰) in carbonates, signifying a change in carbon cycling and seawater chemistry during the interval.…”

Methanogen‐Mediated Precipitation of Mn Carbonates at the Expense of Mn Oxides

“…With the gradual oxygenation of the Earth, some metal oxides such as Mn-oxides appear in the ocean (Hummer et al, 2022;Ostrander et al, 2019). Under low sulfate concentration conditions, these Mn oxides can act as oxidizing agents and react with methane to produce Mn carbonates with extremely negative δ 13 C, which record the Earth's oxygenation events (Cai et al, 2021(Cai et al, , 2023Z. G. Dong et al, 2023).…”

“…With the gradual oxygenation of the Earth, some metal oxides such as Mn‐oxides appear in the ocean (Hummer et al., 2022; Ostrander et al., 2019). Under low sulfate concentration conditions, these Mn oxides can act as oxidizing agents and react with methane to produce Mn carbonates with extremely negative δ 13 C, which record the Earth's oxygenation events (Cai et al., 2021, 2023; Z. G. Dong et al., 2023). However, the direct involvement of Mn oxides in the formation of methanogenesis carbonates which are characterized by extremely positive δ 13 C in pore water has not been documented yet and the corresponding sedimentary record has not been found in the geologic history either.…”