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biases beyond in vivo position relative to the sediment–water interface difficult. There are several implications of these


results. First, Ediacaran taxonomy does not appear to suffer from any litho-preservational barriers among taxa preserved via moldic impressions in siltstone–sandstone grained siliciclastic settings. As discussed, this trend extends into the heavily undersampled carbo- nate facies (e.g., Chen et al. 2014). Second, from a worker effort or “search image” perspective, further explorative work for new Ediacaran localities should remain focused on identifying heterolithic sedimentary packages with sedimentological and structural properties suitable for moldic preservation: abundant MISS, cleavage planes that align with original bedding surfaces, and well-defined bedding soles, which are often formed via contourite and/or turbidity currents (Sperling et al. 2015), and not limited to just siliciclastic sandstone and siltstone lithofacies. Finally, these data may point to the impor-


tance of microbial mats, and not necessarily lithology, in the overall mold-forming process. It is well documented that Ediacaran seafloors were marked by global evidence for extensive microbial mats and absence of deep bioturba- tion (Mángano and Buatois 2014; Davies et al. 2016). These mats would therefore have supported large populations of decay bacteria and created an effective seal over newly buried organisms. This seal would have largely restricted the flux of an oxygenated water column into dysoxic–anoxic pore waters beneath the sediment–water interface, producing geochemical conditions that would heavily favor early diagenetic precipitation of preserving minerals such aspyrite (see above; Darroch et al. 2012). In addition, scavenging and macrophagy are conspicuously absent until the latest Ediacaran, creating ecosystems with minimal biological biostratinomic destruction (Kenchington and Wilby 2014). These conditions have led several authors to suggest the overall fidelity of Ediacaran soft- tissue preservation was vastly superior to that of the Phanerozoic (Brasier et al. 2010). As such, exceptional moldic preservation in the Ediacaran should permit a robust represen- tation of true biological patterns with relatively


few taphonomic biases in comparison with Phanerozoic settings. Furthermore, as microbial mats appear ubiquitous in their temporal, geographic, and bathymetric distribution in the Ediacaran prior to large-scale metazoan bioturbation, the spatial/temporal partitioning of mats as a potential taphonomic bias in the Ediacaran appears largely decoupled from the other factors tested in this study (Laflamme et al. 2011a, 2013). Despite the pervasiveness of the moldic


taphonomic window in the Ediacaran, it is important to note that moldic preservation may exert a bias against epifaunal taxa that extend into the water column (Kenchington and Wilby 2014). Consequently, much of the Ediacaran fossil record is dominated by taxa that are proximal to the sediment–water interface, such as the discoidal taxon Aspidella (Laflamme et al. 2011b), regarded to be the anchoring holdfasts for fronds (Gehling et al. 2000). Rarely are both holdfast and frond preserved on the same bedding surface (e.g., Laflamme et al. 2004; Narbonne et al. 2014: Fig. 4.4). Rather, fronds appear either without associated holdfast in instances where the disk remained buried within the sediment both in vivo and during preservation (Laflamme et al. 2007, 2011b), or more commonly, the frond itself will be absent, leaving only bedding surfaces covered in holdfasts in varying styles of preservation (Tarhan et al. 2010; Kenchington and Wilby 2014). The ubiquity of holdfasts and comparative rarity of preserved fronds is a critical unresolved taphonomic bias present in the current Ediacaran record (Laflamme et al. 2011b). As holdfasts cannot be rigorously correlated with specific frondose taxa (Burzynski and Narbonne 2015), this reinforces that both the diversity and stratigraphic range of frondose taxa are likely highly underrepresented in localities with dense holdfast assemblages (Darroch et al. 2015).


Sampling Intensity and Lithology Limit Carbonaceous Compressions


Although the mid-late Ediacaran macro-


fossil record is dominated by moldic soft-tissue preservation, in several cases carbonaceous


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