Picking out the warp and weft of the Ediacaran seafloor: Paleoenvironment and paleoecology of an Ediacara textured organic surface

The Ediacara Biota, Earth’s earliest ecosystems of complex, macroscopic, multicellular organisms, is preserved in terminal Ediacaran strata worldwide. In the Ediacara Member of South Australia, Ediacara fossil assemblages occur in intimate association with macroscopic, iterative organosedimentary structures, known as “textured organic surfaces” (TOS). These widespread surfaces encompass considerable variability in size and complexity and likely included densely aggregated eukaryotic macroorganisms as well as microbial consortia. The presence of a heterogeneous organic substrate appears to have strongly influenced the ecology of Ediacara benthic ecosystems, and to have fostered the emergence of complex animal-style ecological strategies. Organic substrates may have additionally played an important role in the fossilization of these communities. Systematic sedimentary and paleoecological analysis of approximately 300 square meters of reconstructed fossiliferous bedding planes at Nilpena Ediacara National Park indicates that the distribution of both particular macrofossil taxa and particular TOS appears to be facies-specific. The TOS “weave” exemplifies this facies specificity, and occurs only along rippled sandstone event beds in the Oscillation-Rippled Sandstone Facies. Detailed characterization of the morphology, spatial distribution and sedimentology of weave, as well as distinctive associations with body and trace fossil assemblages, suggest that this TOS is strongly linked to hydrodynamic disturbance. Weave assemblages may therefore provide unique insights into not only Ediacara matground communities but also the local environmental conditions that shaped the ecology and fossilization of Ediacara assemblages. More broadly, the abundance, diversity and facies specificity of TOS suggest that these structures can be used to gauge whether paleoenvironmental and taphonomic conditions favorable for colonization by and preservation of Ediacara macroorganisms were present across a wide range of shallow marine paleoenvironments. TOS may therefore provide a means of constraining whether the absence of Ediacara-type taxa from either older or younger strata is evolutionarily meaningful, and for reconstructing the evolutionary ecology of the Ediacaran-Cambrian transition.