Bioturbation intensity regulated organic carbon and reduced sulfur preservation in middle Paleozoic sediments

Bioturbation plays a key role in regulating organic carbon and reduced sulfur preservation in marine sediments. In modern marine settings, bioturbation fosters higher decomposition rates, decreasing the size of the preserved reactive organic carbon pool, and increases oxygen penetration depths, decreasing pyrite burial. However, the impact of differences in bioturbation intensity (i.e., degree of disruption of sedimentary fabrics) and style (i.e., biodiffusive sediment churning versus bioirrigative flushing of burrows) on these processes remains poorly constrained, particularly for previous intervals of Earth’s history. Here we explore the relationship between bioturbation intensity and both organic carbon and sulfur burial using sedimentary drill cores from Devonian and Carboniferous strata recording oxygenated marine settings in the Appalachian, Antler, Paradox, and Anadarko Basins of North America. Paired, high-resolution measurements of total organic carbon (TOC) and total sulfur (TS) and bioturbation intensity data show that highly bioturbated intervals are consistently characterized by low TOC values. However, lightly to moderately bioturbated strata display TOC values also observed in unbioturbated sediments, suggesting that low to moderate intensities of sediment disruption may not have strongly impacted organic carbon burial in these settings. In contrast, increasing bioturbation at any intensity is associated with decreases in TS, suggesting a strong inverse relationship with pyrite formation. This more quantitative and mechanistic understanding of bioturbation−organic carbon−reduced sulfur relationships provides critical context for reconstruction of the long-term evolution of the global carbon and oxygen cycles, especially during intervals in which bioturbation was less well developed than at present.