Retallack (2014) falsely claims that our conclusions (Gehling and Droser, 2013) are that fossils of the Ediacara Biota are not useful for biostratigraphy. In fact, our conclusions are explicit that it is essential to take taphonomic and environmental conditions into account while evaluating the potential absence (and thus evaluating the stratigraphic range) of a particular taxa. We demonstrate that genera of the Ediacara Biota that were previously thought to have biostratigraphic significance occur in facies co-eval to those that they had been considered to pre- or post-date. This is a very important point when trying to evaluate whether or not taxa have gone extinct or have yet to appear, and how the Ediacara Biota contributes to our understanding of the evolutionary origins of marine organisms on this planet.
Retallack (2014) further suggests that our conclusions were an artifact of “lumping of all frond fossils into one category.” First of all, we included 24 taxa in our table—many of which are not fronds. We included relatively common taxa, most of which occur at other Ediacara localities worldwide. Retallack claims that Pambikalbae (Jenkins and Nedin, 2007) is known from various facies in the Ediacara Member and should have been included. Apart from not being a Rangeomorph and considering that the type material comes from just one bed in a single location, it is impossible to describe this organism as being distributed in “various facies” (Retallack, 2014). We (Gehling and Droser, 2013, our figure 2) illustrated specimens of Charniodiscus and Charnia since they are common.
The discovery of discoidal fossils and Arumberia in the Bonney Sandstone below the Rawsnley Quartzite is used as evidence for this unit being fossiliferous (Retallack, 2014). However, contrary to this and to Jenkins and Nedin (2007), not a single body fossil has ever been illustrated in any facies of the Bonney Sandstone that underlies the Rawnsley Quartzite. This formation consists of red, silty, and micaceous sandstone with desiccation cracks and an array of textured organic surfaces, and is interpreted as a tidal deltaic complex (Gehling, 1982). Arumberia (Glaessner and Walter, 1975) common on red, scoured, silty beds were shown by McIlroy and Walter (1997) to be pseudo-fossils produced by the effect of currents on microbial mats in near-shore settings.
Retallack (2014) refers to papers on “Pound Sandstone” dating from Mawson and Segnit (1949) as a basis for claiming that the Ediacara Member was a coastal-lagoon and intertidal complex. Such papers represented knowledge before any modern concept of process sedimentology and sequence stratigraphy had been applied to these rocks. Moreover, Goldring and Curnow (1967, p. 207) are misinterpreted as they were the first to describe the fossiliferous facies of the Rawnsley Quartzite as representing “a distinct decrease in energy” compared with the higher-energy shallow marine sandstones above. They also regarded the fossil beds as upward shallowing, which is entirely in accord with Gehling and Droser (2013). Gehling (1982, 2000) did basin-wide sedimentological analysis of the Pound Subgroup by mapping out the facies changes from more than 30 measure sections. This work emphasized that the entire Ediacara Member is the sub-marine part of a depositional sequence with thickening and coarsening-upward sedimentary facies that followed a regional rise in sea level, thus infilling a canyon-incised shelf. Not a single body fossil has ever been found or described from the well-studied, and most distinctive, intertidal facies of the Chace Quartzite Member (Gehling, 2000; Gehling and Droser, 2009) or the tidal delta complex of the underlying Bonney Sandstone (Gehling, 1982). If there was any validity to Retallack’s terrestrial hypothesis for the Ediacara Biota, these aforesaid sandstone units should be replete with fossils of the Ediacara Biota. In practice the only biological signatures in the Chace Quartzite Member of the Rawnsley Quartzite and the underlying Bonney Sandstone are textured organic surfaces interpreted as the result of pervasive microbial mats (Gehling and Droser, 2009).
Retallack claims that we (Gehling and Droser, 2013) have changed our interpretation of the Chace Quartzite Member. The Chace Quartzite Member, incised by the Ediacara Member, was referred to as “intertidal sand facies” in Gehling and Droser (2013) and Gehling (1982, 2000). Supratidal facies, bearing the disrupted and domed microbial-mat–bound sand laminae (“petee” structures), are not missing in any section through the Chace Quartzite Member. The concept of “intertidal” includes the range of lower, mid-, and supratidal sand facies. Retallack (2012; 2013, his figure S3) labeled these as examples of “Inga pedotype” bearing specimens of “Cyclomedusa,” and “Warrutu” in other parts of the Brachina Gorge section. However, there is no section in the Flinders Ranges or vicinity where Chace Quartzite and Ediacara Member facies interfinger. It is apparent that Retallack has measured just one partial stratigraphic section on which he has based his interpretation of the Ediacara Member as “terrestrial.” The only portion of the Rawnsley Quartzite that could ever be regarded as “terrestrial” is the supratidal facies of the entirely unfossiliferous Chace Quartzite Member.
Retallack’s hypothesis fails on the basis of sedimentologic and stratigraphic interpretation of an enormously diverse and consistent set of Ediacara Biota body fossils, preserved worldwide.