ASSESSING THE RELATIONSHIP BETWEEN BIOTURBATION INTENSITY AND ORGANIC CARBON PRESERVATION IN MIDDLE PALEOZOIC SEDIMENTS

Bioturbation has long been considered to play an important role in organic carbon preservation potential. In experimental and modern settings, bioturbation has been observed to increase rates of decomposition, leading to a decrease in the size of the preserved reactive organic carbon pool. However, the degree to which this relationship is preserved within the rock record is less well constrained and can be readily confounded by the influence of other factors such as redox state. Additionally, different types of bioturbation may have different effects on organic carbon preservation potential. Bioirrigation, for instance via the active or passive flushing of burrows, can enhance remineralization rates by delivering oxygenated seawater to otherwise anoxic areas of the sediment pile. In contrast, biodiffusive sediment churning can potentially foster increased burial of organic carbon and thus increase preservation potential. Significant questions remain as to how these different styles and intensities of bioturbation may, at the community level, interact with one another to influence the total organic carbon (TOC) content of lithified marine sediments. Here we use Devonian- and Carboniferous-aged cores sampling a range of oxygenated marine settings from the Appalachian and Great Basins to examine the relationship between bioturbation and organic carbon in detail. TOC and other geochemical measurements are paired with high-resolution bioturbation intensity measurements (i.e., ichnofabric index estimation of the extent of sedimentary fabric disruption) and observations of dominant bioturbation styles and burrow types. While unbioturbated or lightly bioturbated strata display a wide range of TOC values, highly bioturbated intervals have exclusively low TOC values, suggesting an important role for intense bioturbation in decreasing the organic carbon preservation in the marine sedimentary record. However, bioturbation-TOC relationships also vary notably across different bioturbation styles, suggesting a more nuanced consideration of these feedbacks may be critical.