Taphonomy of the Ediacaran Fossil Pteridinium Simplex Preserved Three- Dimensionally in Mass Flow Deposits, Nama Group, Namibia Author(s): Mike Meyer , David Elliott , James D. Schiffbauer , Michael Hall , Karl H. Hoffman , Gabi Schneider , Patricia Vickers-Rich , and Shuhai Xiao Source: Journal of Paleontology, 88(2):240-252. 2014. Published By: The Paleontological Society DOI: http://dx.doi.org/10.1666/13-047 URL: http://www.bioone.org/doi/full/10.1666/13-047 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Journal of Paleontology, 88(2), 2014, p. 240–252 Copyright Ó 2014, The Paleontological Society 0022-3360/14/0088-0240$03.00 DOI: 10.1666/13-047 TAPHONOMY OF THE EDIACARAN FOSSIL PTERIDINIUM SIMPLEX PRESERVED THREE-DIMENSIONALLY IN MASS FLOW DEPOSITS, NAMA GROUP, NAMIBIA MIKE MEYER,1,5 DAVID ELLIOTT,2 JAMES D. SCHIFFBAUER,3 MICHAEL HALL,2 KARL H. HOFFMAN,4 GABI 4 2 1 SCHNEIDER, PATRICIA VICKERS-RICH, AND SHUHAI XIAO 1Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA, ,[email protected].; ,[email protected].; 2School of Geosciences, Monash University, Clayton, Victoria, 3800, Australia, ,[email protected].; ,[email protected].; 3Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA, ,[email protected].; 4Geological Survey of Namibia, Windhoek, Namibia, ,[email protected].; ,[email protected].; and 5Department of Geosciences and Natural Resources, Western Carolina University, Cullowhee, NC 28723, USA, ,[email protected]. ABSTRACT—Ediacara-type fossils are found in a diverse array of preservational styles, implying that multiple taphonomic mechanisms might have been responsible for their preservational expression. For many Ediacara fossils, the ‘‘death mask’’ model has been invoked as the primary taphonomic pathway. The key to this preservational regime is the replication or sealing of sediments around the degrading organisms by microbially induced precipitation of authigenic pyrite, leading toward fossil preservation along bedding planes. Nama-style preservation, on the other hand, captures Ediacaran organisms as molds and three-dimensional casts within coarse-grained mass flow beds, and has been previously regarded as showing little or no evidence of a microbial preservational influence. To further understand these two seemingly distinct taphonomic pathways, we investigated the three-dimensionally preserved Ediacaran fossil Pteridinium simplex from mass flow deposits of the upper Kliphoek Member, Dabis Formation, Kuibis Subgroup, southern Namibia. Our analysis, using a combination of petrographic and micro-analytical methods, shows that Pteridinium simplex vanes are replicated with minor pyrite, but are most often represented by open voids that can be filled with secondary carbonate material; clay minerals are also found in association with the vanes, but their origin remains unresolved. The scarcity of pyrite and the development of voids are likely related to oxidative weathering and it is possible that microbial activities and authigenic pyrite may have contributed to the preservation of Pteridinium simplex; however, any microbes growing on P. simplex vanes within mass flow deposits were unlikely to have formed thick mats as envisioned in the death mask model. Differential weathering of replicating minerals and precipitation of secondary minerals greatly facilitate fossil collection and morphological characterization by allowing Pteridinium simplex vanes to be parted from the massive hosting sandstone. INTRODUCTION et al., 2000). While Fermeuse-style preservation was previously DIACARA FOSSILS (580–542 Ma) are some of the earliest suggested to have less influence from microbial mats due to its E known complex multicellular life forms but have enigmatic deeper water paleoenvironmental setting (e.g., Narbonne, 2005), taphonomic histories and phylogenies. Four preservational recent investigation shows that three-dimensionally preserved styles falling under the Ediacara-type preservation umbrella Aspidella in the Fermeuse Formation is surrounded by fine- have been described as the classic taphonomic modes of the grained clay material representing biofilm envelopes (Laflamme Ediacaran Period (Fig. 1). Flinders-style death-mask preserva- et al., 2011b). Finally, Conception-style preservation (‘‘Ediacar- tion (Fig. 1.1), characteristic of most Ediacara fossiliferous beds an Pompeii’’; Fig. 1.4) results from the burial of benthic in the Flinders Ranges of South Australia (and some facies in organisms beneath volcanic ashes, as is observed in the the White Sea Region of Russia), captures epibenthic organisms Conception Group of Newfoundland and the Charnwood that lived in shallow, photic zone environments between normal succession of England (Seilacher, 1992; Narbonne, 2005). and storm wave-base (Gehling and Droser, 2013). This In addition to these ‘‘classic’’ styles, other preservational preservational regime was dependent on event deposition of modes have also added important details to Ediacaran storm beds and lithification aided by microbial communities taphonomic descriptions. These include three-dimensional (Gehling, 1999; Narbonne, 2005). Three-dimensional Nama- pyritization of the Gaojiashan biota (Cai et al., 2010, 2012), style preservation (Fig. 1.2), characteristic of the Kuibis and aluminosilicification and kerogenization of the Doushantuo and Schwarzrand subgroups of Namibia, entombs organisms within mass-flows or storm event sediments as opposed to preservation Dengying formations (Anderson et al., 2011; Cai et al., 2012; under event sediments at the base of the event bed (Jenkins, Meyer et al., 2012), three-dimensional phosphatization of 1992; Narbonne, 2005; Vickers-Rich, 2007; Vickers-Rich et al., cellularly preserved microfossils in the Doushantuo Formation 2013). Fermeuse-style preservation (Fig. 1.3) represents deeper (Xiao and Knoll, 2000; Xiao and Schiffbauer, 2009; Schiffbauer water assemblages found in outer shelf, slope, or basinal et al., 2012), carbonaceous compression of macroalgae in the paleoenvironments, and is known from the Fermeuse Formation Doushantuo Formation (Xiao et al., 2002; Yuan et al., 2011), as of Newfoundland, the Windermere Supergroup of northwestern well as silicification of microfossils in Doushantuo chert Canada, and the Innerelv Member of northern Norway nodules of South China (Xiao et al., 2010). While this diversity (Narbonne and Hofmann, 1987; Farmer et al., 1992; Gehling of preservational modes has greatly increased our understanding 240 MEYER ET AL.—3-D TAPHONOMY OF THE EDIACARAN FOSSIL PTERIDINIUM SIMPLEX 241 FIGURE 1—Representatives of different Ediacara-type preservational styles. 1, Flinders-style; two Dickinsonia specimens from the Flinders Range and on display at the South Australian Museum, Adelaide, Australia; 2, Nama-style; Namibian Pteridinium specimens jumbled together in a hand sample, NGSF383.F/ PVR2003; 3, Fermeuse-style; Aspidella from the Fermeuse Formation, Newfoundland; photo courtesy of M. Laflamme; 4, Conception-style; Ediacara-type fossils preserved beneath a volcanic ash layer (arrow), Mistaken Point Formation, Newfoundland; Photo courtesy of Alan J. Kaufman. Scale bar in 1¼2 cm; 2¼5 cm; 3¼2 cm; and 4¼5 cm. of Ediacaran biodiversity and ecology, the taphonomic process- deposited in shallow-water environments where Ediacara fossils es of many Ediacaran fossil localities remain enigmatic. are preserved, and whether such clays are of detrital, authigenic, One of the most important findings in recent taphonomic metamorphic, or weathering origin. investigations is the association of clay minerals in Ediacaran For many Ediacara fossils found in coarse- and fine-grained fossil preservation (Anderson et al., 2011; Laflamme et al., siliciclastic rocks, some variation of the death mask hypothesis 2011b; Cai et al., 2012; Meyer et al., 2012), an association that (Gehling, 1999; Narbonne, 2005) has been invoked as the hasalsobeenknownfromPhanerozoicBurgessShale-type primary taphonomic pathway. This hypothesis proposes that (BST) preservational windows. For example, the association of authigenic pyrite precipitation just beneath microbial mats that clays with exceptionally preserved Ediacaran fossils have been colonized bedding surfaces can preserve both microbial mat previously documented in carbonaceous compressions in the texture (Gehling and Droser, 2009; Laflamme et al., 2011a) and Ediacaran successions of South China (Anderson et al., 2011; organisms associated with the mats (Gehling, 1999). The death Caietal.,2012)andinAspidella from the Fermeuse Formation mask taphonomic process relies on storm events