THE ECOSYSTEMS TO BE ENGINEERED: SETTING A BASELINE FOR THE NATURE OF SUBSTRATES IN THE PRECAMBRIAN TO CONSTRAIN THE IMPACT OF THE AGRONOMIC REVOLUTION

Bioturbation is a primary mechanism of ecosystem engineering that was integral to the establishment of modern marine environments. A large body of research focuses on the transition from the Precambrian—characterized by a lack of bioturbation-related ecosystem engineering and corresponding anactualistic sedimentological features related to the dominance of organic mats—to the Cambrian, characterized by the radiation of complex burrowing behaviors. As a result, much knowledge has been gained pertaining to the timing and extent of bioturbation changes and their impact on ocean geochemistry and animal evolution. However, these insights, which are informed by the juxtaposition of the Precambrian and Cambrian sedimentological records, rely on the assumption that we possess a complete understanding of the impact that Precambrian matgrounds had on sedimentation processes in clastic shelfal environments and on the resultant stratigraphic record. This is not the case; in fact, the baseline sedimentological conditions that existed in the Precambrian have few constraints beyond a general understanding of their stabilization by organic mat surfaces. To fully appreciate the impact that the earliest bioturbators had on the ecosystems that they engineered, we must first understand the nature of the substrate and sediment deposition that existed before they arrived. To this end, we examine the microstratigraphy of the Ediacara Member, South Australia (~550 Ma) in multiple sections exposed at the Nilpena Ediacara National Park (NENP). This builds on Tarhan et al. 2017—who defined the anactualistic nature of this record through a two-dimensional lens—by providing a detailed picture of sedimentological dynamics in the three-dimensional context of excavation pits at NENP. Viewed through this lens, the Ediacaran shallow shelf stratigraphic record is characterized by geologically rapid successions of depositional events ranging in thickness from the sub-mm to cm scale and are discontinuous over the span of meters. This is distinct from that of the Cambrian, which is characterized by laterally continuous, thick-bedded sandstone event deposits. This distinction in stratigraphic architectures encapsulates the extent of the impact of matgrounds on Precambrian substrate dynamics that will be explored in this talk.