HOW BIOGEOCHEMICALLY IMPACTFUL WAS SKOLITHOS PIPEROCK? NEW INSIGHTS FROM CAMBRIAN FIELD DATA AND GEOCHEMICAL MODELING (Invited Presentation)

The advent of bioturbation in the early Paleozoic and the subsequent intensification of sediment mixing by benthic organisms have long been considered to have dramatically altered marine ecosystems and biogeochemical cycling. However, the timing and pace of the transition to near-ubiquitous well-bioturbated seafloor sediments remain debated. Skolithos “piperock,” a classic Cambrian ichnofabric composed of densely packed vertical burrows, has often been invoked as evidence for an early ramping up of seafloor colonization and intense sediment disruption by burrowing animals. However, the biogeochemical impact of Skolithos piperock has not been quantitatively explored in this context. Here, we relate high-resolution sedimentological and bioturbation data from the Zabriskie Quartzite of the Death Valley region of California—a unit well-known for its piperock—to a new numerical three-dimensional diagenetic model to investigate the effect of Skolithos on sediment oxygenation, organic carbon remineralization and sulfur oxidation. Our modeling indicates that increasing Skolithos burrow density would have substantially expanded local oxygen penetration depths in nearshore sandy environments. Over ecological time scales, Skolithos piperock may therefore have fostered greater seafloor habitability for a range of macroorganisms. Concurrently, Skolithos piperock, by shifting the balance of aerobic and anaerobic pathways of organic carbon remineralization, potentially contributed to seawater deoxygenation over geologic time scales. However, our field data indicate true piperock is relatively scarce in the Zabriskie Quartzite, even among stratigraphic packages of the same lithofacies as piperock-hosting intervals. This suggests that, in the Zabriskie and potentially other Cambrian piperock-bearing units, the broader impact of piperock on seafloor ecology, chemistry, and sediment properties may have been restricted in scope.