PICKING OUT THE FABRIC OF THE EDIACARA SEAFLOOR: EVIDENCE OF WIDESPREAD, HETEROGENEOUS TEXTURED ORGANIC SURFACES

The Ediacara Biota—Earth’s earliest complex, macroscopic communities—is recorded in exceptionally preserved fossil assemblages of soft-bodied organisms. Ediacara Biota fossil assemblages are found around the world and are commonly abundant where they occur. In the Flinders Ranges in South Australia, the eponymous Ediacara Member of the Rawnsley Quartzite contains an abundant and richly diverse Ediacara fossil assemblage. To date, over thirty-five fossiliferous beds, as well as numerous, discontinuous veneer-like bedforms (“shims”), of Ediacaran-aged rock have been excavated from multiple successions at the Nilpena National Heritage fossil site. In addition to the thicker (cm-scale), fossiliferous beds that have been excavated, several thinner (down to sub-mm-scale) shims, were also uncovered. The excavation of these beds has enabled the systematic and spatially extensive study of in-situ Ediacara communities, in tandem with detailed characterization of their bed-scale sedimentology and taphonomy. Ediacara bedding planes are not only characterized by diverse assemblages of discrete macrofossils, but are also densely covered by a diverse assortment of iterative organosedimentary textures, known as textured organic surfaces (TOS). TOS record the interaction of densely packed assemblages of organisms, including macroscopic, eukaryotic-grade organisms such as the tubular fossil Funisia, with sedimentary processes. TOS are a ubiquitous component of the Ediacara seafloor, and occur on all excavated beds and shims at Nilpena. TOS are characterized by a heterogeneity on par with that of Ediacara macrofossil assemblages, and contributed significantly to the diversity and ecological complexity of the Ediacara seafloor. Although microbial mats have long been considered an important component of the Precambrian biosphere, the ubiquity, heterogeneity and complexity of TOS far surpasses that known from the pre- and post-Ediacaran stratigraphic records.