EDIACARAN DISTRIBUTIONS IN SPACE AND TIME


compressions have been recovered. The most well-known instances of this occur in several Chinese localities, including the Gaojiashan Lagerstatte, Shaanxi Province (Cai et al. 2012), and the Miaohe and Wenghui biotas in the Hubei and Guizhou provinces, respectively (Xiao et al. 2002; Zhao et al. 2004) (Fig. 3: [Gaoj], [Miah1], [Jiang]). Carbonaceous compressions, formed via kerogenization (polymerization of organic molecules), are best known from the iconic Cambrian Burgess Shale; hence they are often referred to as Burgess Shale–type (BST) preservation (Orr 2014). Kerogenization is essential to BST preservation; however, it can be accompanied by two other miner- alization processes: authigenic pyritization and aluminosilicification, which can co-occur as a range of taphonomic end members that together contribute to the BST taphonomic mode (Cai et al. 2012; Schiffbauer et al. 2014). Database analysis has shown significant undersampling of fossiliferous shale litho- facies, identifying only 6 BST candidates from our 86 Ediacaran localities and >45 geological units: [Ong], [MatoGDS], [Jiang], [Gaoj], [Kh_khat],and [Miah1] (Fig. 3). These deposits all form in low-energy, deep-water distal offshore shelves or restricted basinal lagoons. Perhaps the most uncertain feature of Ediacaran BST deposits is the apparent exclusion of frondose taxa from this preserva- tional window (Steiner and Reitner 2001; Grazhdankin et al. 2008). The Khatyspyt Formation in Siberia [Kh_khat] is interpreted to be a distal, low-energy carbonate ramp, below storm-weather wave base (SWWB). Although it contains exquisitely preserved Rangeomorphs such as Charnia Ford, 1958, occurring as molds in authigenic carbonate cementation, these same frondose taxa are relegated to “phantoms” within inter- bedding carbonaceous compression windows (Grazhdankin et al. 2008: Fig. 3a–h). New Ediacaran localities with BST-type preserva- tion may therefore help to confirm the presence/absence of certain Ediacaran taxa from this mode of preservation, thus resolving issues associated with taphonomic effect versus ecological biofacies (Zhu et al. 2008; Gehling and Droser 2013; Kenchington and Wilby 2014; Carbone et al. 2015).


583 Temporal Distribution of Ediacara Biota


Chronostratigraphic Overlap of the Avalonian and White Sea Assemblages


Evolutionary succession has often been suggested as an important factor in the distribution of taxa in the Ediacaran macrofossil record. However, the ability to test the biotic assemblages as discrete temporal intervals has been limited by a lack of high-quality geochronology. We use a collection of updated publication data to reanalyze Waggoner’score assemblage concept as temporally distinct by binning Ediacaran localities into the traditionally accepted biostratigraphic intervals for the Avalon (579–559Ma), White Sea (558–550Ma), and Nama (549–541Ma) (Narbonne et al. 2012; see Supplementary Table S.5). If the hypothesis that the three assemblages represent a response to a temporal control on the distribution is correct, then temporal binning should also display a clear polygonal separation similar to the initial taxonomic separation (Fig. 1). Instead, NMDS ordination plots of time-binned localities reveal that temporal overlap is present between both the Avalon–White Sea andWhite Sea–Nama assemblages. These results agree with the current, albeit limited geochronological record (Fig. 4, discussed below), and are supported by beta-diversity (dissimilarity) metrics showing that temporal binning pro- duces the lowest diversity dissimilarity when compared with all other variables being tested (Table 2). However, upon further statistical analyses, the data produce contradictory results. When confidence ellipses were drawn around the class centroids for each time bin, they did not overlap, suggesting the assemblages are in fact temporally distinct at CI=95% (Supplementary Fig. S.4.D). These inconsistent resultsmay reflect differences in therelativesamplesizeoftested variables: abundant diversity data yield higher degrees of confidence and therefore a narrower overall confidence interval, while the limited number of geochronological dates requires significantly wider confidence intervals (see Supplementary Table S.5). At present, both NMDSandbeta-diversitydata support previous local-scale observations of contemporaneous but unrelated taxa partitioning into different depositional environments (Grazhdankin 2004;


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