EDIACARAN OCEAN CHEMISTRY: INSIGHTS FROM MULTIPLE SULFUR ISOTOPE MEASUREMENTS OF PAIRED SULFATE- PYRITE IN THE HUQF SUPERGROUP, OMAN

Earth’s surface environments, its biology and its ecology underwent a series of dramatic changes between the Ediacaran and early Cambrian (635Ma to 540Ma). The Ediacaran deep oceans are thought to have experienced a stepwise oxygenation and some eukaryotic organisms appeared and diversified during the second and third stages of this oxygenation. This idea is support by the high resolution isotope records of carbon and sulfur in the Huqf Supergroup, Oman. The Shuram negative carbon isotope excursion (~580Ma) is interpreted to record the extensive oxidation of a deep organic matter reservoir and is thought to be the start of the second stage of oxygenation. The isotopic records of the difference between oceanic sulfate and sedimentary sulfur (d³⁴S) showed a general increasing fractionation, which is interpreted to reflect the growth of the oceanic sulfate reservoir (Fike et al, 2006).

We present new sulfur isotope measurements (δ³⁴S and Δ³³S) of carbonate associate sulfate (CAS) and sedimentary pyrite(CRS) from Oman, previously studied by Fike et al. (2006) and Fike et al. (2008) to explore the dynamics and response of the marine sulfur cycle. We document covariation between δ³⁴S and Δ³³S for carbonate associated sulfate (CAS) and also for coexisting Cr-reducible sulfide (CRS).

Model calculations show that the changes in the fraction of sulfur recycled from the sediments by re-oxidation and exchange between porewater and seawater sulfate can explain this isotopic variation. Our results are consistent with prior models based on other criteria that suggest a link between oceanic sulfate concentrations and reoxidation plus porewater-seawater exchange. Our model also shows that while the fraction of pyrite burial (fpy) has a control on the isotopes, other factors such as reoxidation and exchange between sediment porewater and oceanic pools have a larger one that can be shown with Δ³³S.