EDIACARAN LIFE CLOSE TO LAND: COASTAL AND SHOREFACE HABITATS OF THE EDIACARAN MACROBIOTA, THE CENTRAL FLINDERS RANGES, SOUTH AUSTRALIA

The Rawnsley Quartzite of South Australia hosts some of the world’s most diverse Ediacaran macrofossil assemblages, with many of the constituent taxa interpreted as early representatives of metazoan clades. Globally, a link has been recognized between the taxonomic composition of individual Ediacaran bedding plane assemblages and specific sedimentary facies. Thorough characterization of fossil-bearing facies is thus of fundamental importance for reconstructing the precise environments and ecosystems in which early animals thrived and radiated, and distinguishing between environmental and evolutionary controls on taxon distribution. This presentation gives a refined palaeoenvironmental interpretation of the Rawnsley Quartzite sedimentary facies. Our analysis suggests that previously inferred water depths for fossil-bearing facies are overestimations. In the central regions of the outcrop belt, rather than shelf and submarine canyon environments below maximum (storm-weather) wave base, and offshore environments between effective (fair-weather) and maximum wave base, the succession is interpreted to reflect the vertical superposition and lateral juxtaposition of unfossiliferous non-marine environments with fossil-bearing coastal and shoreface settings. Whilst facies containing body fossils of the Ediacaran macrobiota remain definitively marine, horizontal surface trace fossils in the foreshore facies represent the earliest known evidence of mobile organisms in intermittently emergent environments. Our revised shoreface and coastal framework creates greater overlap between this classic ‘White Sea’ biotic assemblage and those of younger, relatively depauperate ‘Nama’-type biotic assemblages located in Namibia. Such overlap lends support to the possibility that the apparent biotic turnover between these assemblages may reflect a genuine evolutionary signal, rather than the environmental exclusion of particular taxa.