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Studies phosphatized biotas from the Neoproterozoic Doushantuo Formation on the Yangtze Platform. Multiple taphonomic windows contained in the cherts, carbonaceous shales and phosphorites onto the late Neoproterzoic biosphere; Clear phophatic window; Preservation of a multitude of single-celled eukaryotes, multicellular algae and microscopic animals.

Arising from: J. V. Bailey, S. B. Joye, K. M. Kalanetra, B. E. Flood & F. A. Corsetti 445, 198–201 (2007); Bailey et al. replyBailey et al. propose that the Ediacaran microfossils Megasphaera and Parapandorina, previously interpreted as animal resting eggs and blastula embryos, represent Thiomargarita-like sulphide-oxidizing bacteria, claiming that this interpretation better explains their abundance and taphonomy. Here we highlight important observations that significantly weaken the authors' conclusions. [ABSTRACT FROM AUTHOR]

Orbisiana is an Ediacaran fossil characterized by linearly arranged circular or cylindrical units. The genus was first described from the late Ediacaran Redkino Series in the Moscow Syncline of Russia where it is preserved as pyritic molds in siltstone. Here we report Orbisiana linearis , originally described as Seirisphaera lineare , from black shale of the early Ediacaran Lantian Formation in South China. Unlike the type species ( O. simplex ), O. linearis is preserved as carbonaceous compressions on the bedding surface, with rare specimens preserved three-dimensionally, allowing morphological characterization using X-ray microCT techniques. Morphological, paleoecological and taphonomic analysis suggests that O. linearis was a chain-like modular organism characterized by uniserially arranged, millimeter-sized, and tangentially contacting circular or cylindrical units. Ontogenetic growth of O. linearis was likely achieved through both accretionary addition of new modules and inflational expansion of existing units, and it appears that inflational growth was determinate. Although its phylogenetic affinity remains uncertain, O. linearis was likely a procumbent epibenthic or semi-endobenthic organism that lived on the seawater-sediment interface or partly buried in sediments. O. linearis in the Lantian Formation was preserved in situ, although some specimens are disarticulated and many are tectonically deformed. Orbisiana joins a growing list of Ediacaran genera that have a remarkable range of stratigraphic, environmental, ecological, and taphonomic distribution. [ABSTRACT FROM AUTHOR]

Pyritization represents a major taphonomic pathway for exceptional preservation of soft tissues. Although various Ediacaran Lagerstätten contain pyritized fossils, the controls on this taphonomic pathway prior to the Precambrian-Phanerozoic transition have only recently received significant attention, and no studies have yet thoroughly investigated environmental conditions facilitating exceptional preservation via pyritization in the early Ediacaran. Here, we investigate the preservational environments of macroscopic fossil Chuaria in the early Ediacaran Lantian Formation of South China using petrographic, electron microscopic, and geochemical data. Chuaria occur as pervasively pyritized (spheroid-shaped) globose and non-pervasively pyritized (disk-shaped) subglobose fossils in different stratigraphic intervals. Although these different stratigraphic intervals are similar in terms of total sulfur (TS, ~ 5%), subglobose Chuaria shales have greater total organic carbon (TOC, ~ 7.9%) contents than globose Chuaria shales (~ 3.6%). Additionally, petrographic observations and TOC-TS cross-plots suggest that, whereas globose fossils were preserved under suboxic bottom waters, the subglobose fossils were preserved in euxinic bottom waters. Overall, these results affirm that pyritization in the Precambrian was generally favored in organic-poor, reactive iron-rich, sulfate-rich environments probably with slow sedimentation rates. When organics were scarce and reactive iron was abundant, bacterial sulfate reduction (BSR) created hydrogen sulfide and reactive iron concentration gradients around fossils, which kinetically and thermodynamically favored rapid and pervasive pyritization, as observed in globose Chuaria . Conversely, when organics were abundant and reactive iron/sulfate availabilities were limited by widespread BSR, fossils were relatively rapidly buried beneath the BSR metabolic zone of sediment, where they were principally preserved as aluminosilicified carbonaceous fossils that were compacted into subglobose forms. Thus, preservational variations among pyritized fossils in the Ediacaran may reflect differences in sedimentary organic matter content and/or bottom water redox chemistry. [ABSTRACT FROM AUTHOR]

Abstract: A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Member limestone of the upper Ediacaran Dengying Formation, Yangtze Gorges area, South China. It is characterized by horizontal tunnels connected with short vertical burrows and surface trails. The horizontal burrows are elliptical or bilobed in transverse cross-section, preserved in full relief, and filled with carbonate intraclasts, micrites, as well as calcite and silica cements. They occur exclusively in silty, crinkled, and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats; no burrows have been found in intraclastic layers adjacent to the microlaminated layers. The vertical traces are filled with the same material as the burrows, but they typically project through the crinkled microlaminae and are exposed on the bedding surface. The surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs. The burrow infill has δ18Ocarb and δ13Ccarb values distinct from, but intermediate between, microlaminated and intraclastic layers, consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements, intraclasts, and micrites. Bedding plane bioturbation intensity (20–40%)—measured as percentage of bedding plane area covered by L. trevallis traces—is comparable to similar measurements in pre-trilobite Cambrian carbonates. The exclusive occurrence of L. trevallis within microbial mats may have both taphonomic and ecological significance. These mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows, and they may have also facilitated early diagenetic cementation of burrow infill, thus facilitating burrow preservation. The close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources. The trace makers of L. trevallis were better able to utilize the resources around them than many other Ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late Ediacaran oceans at the dawn of the agronomic revolution. [Copyright &y& Elsevier]

• Preservation mode of the Ediacaran Chuaria fossils from the Lantian biota was revisited. • Mixed quartz and Mg-rich aluminosilicates envelope the pyritized fossils. • The enveloped minerals are secondary overgrown, playing no contribution to the initial soft tissue fossilization. The Chuaria is the most common fossils in the Ediacaran Lantian biota (approximately 600 Ma) of South China which represents one of the earliest-known macroscopic eukaryotic fossil assemblages with high morphological diversity. Although great majority of the Lantian Chuaria fossils are preserved as carbonaceous compressions, Chuaria has been reported to be commonly preserved as pyritization enveloped by aluminosilicate minerals in the upper Member II of the Lantian Formation. The outer minerals that envelope the pyrite layer have been assigned to quartz or aluminosilicate clay minerals. However, their exact mineral compositions as well as whether these minerals have contributed to the exceptional preservation of Ediacaran Lantian Chuaria , remain unclear. We employed light microscopy, field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy techniques to revisit the preservation of pyritized Chuaria from the Lantian biota. Our taphonomic experiments show that pyritized Chuaria fossils are enveloped by platy minerals that are a complex mixture of quartz and magnesium-rich aluminosilicates. Integrated mineral and structural pattern analyses show that these quartz and clay minerals are both secondary overgrowth on Chuaria internal mold, which probably formed as a diagenetic product concurrent with carbonate dissolution in the Lantian black shales. Their formation is probably regulated by local micro-environment near the Chuaria bodies. These enveloped minerals may facilitate preservation and identification of Chuaria fossils, but they are probably not involved in the initial fossilization process as the early diagenetic pyritization has done. [ABSTRACT FROM AUTHOR]