EDIACARAN DISTRIBUTIONS IN SPACE AND TIME


siliciclastic sandstone and siltstone dominate the Ediacaran fossil record (Gehling 1999; Gehling et al. 2005).Moldic preservation occurs through a complex interplay between two processes: (1) mold formation initiates as labile tissues decay rapidly and are infilled with sediment; and (2) sulfate-reducing bacteria then exploit this decaying organic material, converting sulfate (SO4


581 2-) to hydrogen sulfide (H2S),which


combines with iron in the sediment to precipi- tate early diagenetic minerals such as pyrite (FeS2). Ultimately, these molds are believed to be the product of multiple depositional factors at the time of burial, including presence of clay minerals,microbialmat prevalence, and ensuing chemistry of pore waters (Narbonne 2005; Callow and Brasier 2009; Darroch et al. 2012, Kenchington and Wilby 2014). In light of this complexity, we instead tested the degree to which overall preserving lithology affects this taphonomic character in order to inform potential outcrop-scale biases in collection methods. Database results reinforce a clear ubiquity of moldic preservation across Ediacaran genera;


convex hulls for each lithology show limited separation toward any of the traditional assemblages, perhaps with the exception of the Avalonian biota, which are tightly correlated with Conception-style preservation in ash (Fig. 3, Supplementary Fig. S.4.C). This inference is strengthened by the results of beta-diversity analyses, which show that lithology accounts for the second-lowest dissimilarity values among tested variables after temporal binning (Table 2). Although moldic preservation may appear to create a taphonomic filter for epifaunal taxa (Kench- ington and Wilby 2014), with the exception of the unique Conception-type, moldic preser- vational styles are observed in a wide range of paleoenvironments (shallow shoreface to deep-water slope; see Bouougri et al. 2011; Narbonne et al. 2014). Furthermore, moldic preservation appears to be largely decoupled from any strictly lithological controls, such as carbonate facies (Grazhdankin et al. 2008; Chen et al. 2014; Fig. 3, [Kh_khat] and [Muz2Sh]). This can make the identification of any major taxonomic–taphonomic moldic


FIGURE 3. Distribution of macrofossil-preserving lithologies at each locality, overlain as polygons across our updated taxonomic ordination space. Siliciclastic coarse-grained sandstone (Coarse sandstn.), fine-grained siltstone (Mixed siltstn.), and limestones (Limestone) appear broadly distributed across taxa, while siliciclastic and carbonate shale/ mudstones (Shale/mudstn.) and ash (Ash) show greater taxonomic restriction.


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