Possible evidence of primary succession in a juvenile-dominated Ediacara fossil surface from the Flinders Ranges, South Australia

Ediacara fossil surfaces from the Flinders Ranges (South Australia) commonly record excellent preservation quality and can provide a palaeoecological window into some of the oldest communities on Earth (ca. 555 Ma). An excavated semi-contiguous sandstone bed of 6.5 m(2) from a fossil locality at Crisp Gorge in the central Flinders Ranges records an abundance of taxa and structures characteristic of White Sea assemblage communities. Stratigraphic analysis places the fossil surface within the Oscillation Rippled Sandstone Fades of the Ediacara Member at Crisp Gorge. The community appears to be predominantly juvenile forms, with Dickinsonia costata, Parvancorina minchami and Tribrachidium heraldicum present only within interpreted juvenile size ranges. The textured organic surface contains structures including low relief ridges and round bosses, but overall records a smooth bed surface and is interpreted as representing a surface with only an immature microbial mat developed before burial. No effaced or decayed organisms were identified. Community analysis describes an intermediate Shannon diversity (1.27) and an uneven community dominated by the population of D. costata, which comprises more than 50% of the individuals. The examined parameters, when combined with the presence of small, juvenile taxa and an immature organic mat, suggests that the community inhabiting this surface prior to its catastrophic burial may have been comparable to a modern early-stage, primary successional community. The Crisp Gorge bed emphasizes that Ediacara fossil surfaces from South Australia span a range of developmental stages and offer a window into Ediacaran sea-floor communities at various stages of maturity. (C) 2017 Elsevier B.V. All rights reserved.