A NEOICHNOLOGICAL APPROACH TO EXAMINING POTENTIAL DRIVERS OF EDIACARAN-CAMBRIAN GEOBIOLOGICAL CHANGE

The Ediacaran-Cambrian transition (‘ECT’, ~574-539 Ma) represents a fundamental step-change in the complexity of Earth systems, recording perturbations to global geochemical cycles, a permanent change in the character of the sedimentary record, and the emergence of macroscopic animal-dominated ecosystems. While fossil and geological record for these paradigm shifts is generally well documented, the ultimate causes for many of these phenomena remain contentious and poorly understood. One hypothesized driver of geobiological change over the ECT involves the late Ediacaran evolution of animal-driven sediment disturbance and reworking (‘bioturbation’) and its downstream effects; these include changes in pore water chemistry, a decrease in seafloor microbial mat cover, and an increase in subsurface sediment oxygenation. However, there remains a dearth of empirical data regarding the mechanisms, structures, and potential impacts of intense bioturbation across the ECT.

Here we describe a neoichnological approach to quantifying the sedimentological and geochemical impacts of bioturbation by the modern priapulid worm Priapulus caudatus. Priapulids are thought to have remained largely unchanged since their appearance in the Ediacaran-Cambrian and are heavily implicated as potential agents of ECT change. Preliminary experimental work allows us to observe priapulid burrowing, quantify rates of sediment homogenization, and measure the downward transport of nutrient proxies. We thus detail these early results and outline ongoing endeavors that are constructing a more complete picture for how priapulids – in addition to other tracemaking organisms – may have driven geobiological change over the ECT.