Abstract Reconstructions of ancient sulfur cycling and redox conditions commonly rely on sulfur isotope measurements of sedimentary rocks and minerals. Ediacaran strata (635–541 Ma) record a large range of values in bulk sulfur isotope difference (Δ34S) between carbonate-associated sulfate (δ34SCAS) and sedimentary pyrite (δ34Spy), which has been interpreted as evidence of marine sulfate reservoir size change in space and time. However, bulk δ34Spy measurements could be misleading because pyrite forms under syngenetic, diagenetic, and metamorphic conditions, which differentially affect its isotope signature. Fortunately, these processes also impart recognizable changes in pyrite morphology. To tease apart the complexity of Ediacaran bulk δ34Spy measurements, we used scanning electron microscopy and nanoscale secondary ion mass spectrometry to probe the morphology and geochemistry of sedimentary pyrite in an Ediacaran drill core of the South China block. Pyrite occurs as both framboidal and euhedral to subhedral crystals, which show largely distinct negative and positive δ34Spy values, respectively. Bulk δ34Spy measurements, therefore, reflect mixed signals derived from a combination of syndepositional and diagenetic processes. Whereas euhedral to subhedral crystals originated during diagenesis, the framboids likely formed in a euxinic seawater column or in shallow marine sediment. Although none of the forms of pyrite precisely record seawater chemistry, in situ framboid measurements may provide a more faithful record of the maximum isotope fractionation from seawater sulfate. Based on data from in situ measurements, the early Ediacaran ocean likely contained a larger seawater sulfate reservoir than suggested by bulk analyses.
Abstract The early E diacaran L antian F ormation in S outh C hina contains some of the oldest known representatives of morphologically complex macroorganisms, including various macroalgae and putative animals. The macroalgal fossils have been described previously in several publications, but no taxonomic treatment has been published for the putative animal fossils. This hampers our ability to fully evaluate and communicate the significance of these potentially important E diacaran macrofossils. To address this deficiency, here we provide a systematic description of these putative animal fossils from the L antian F ormation, including four new genera and five new species: L antianella laevis gen. et sp. nov., L . annularis gen. et sp. nov., P iyuania cyathiformis gen. et sp. nov., Q ianchuania fusiformis gen. et sp. nov. and X iuningella rara gen. et sp. nov. Morphological comparisons of these fossils and potential modern analogues are provided and critically assessed.
Abstract The end-Permian mass extinction (EPME; ca. 252 Ma) led to profound changes in lacustrine ecosystems. However, whether or not post-extinction recovery of lacustrine ecosystems was delayed has remained uncertain, due to the apparent rarity of Early and Middle Triassic deep perennial lakes. Here we report on mid–Middle Triassic lacustrine organic-rich shales with abundant fossils and tuff interlayers in the Ordos Basin of China, dated to ca. 242 Ma (around the Anisian-Ladinian boundary of the Middle Triassic). The organic-rich sediments record the earliest known appearance, after the mass extinction, of a deep perennial lake that developed at least 5 m.y. earlier than the globally distributed lacustrine shales and mudstones dated as Late Triassic. The fossil assemblage in the organic-rich sediments is diverse and includes plants, notostracans, ostracods, insects, fishes, and fish coprolites, and thus documents a Mesozoic-type, trophically multileveled lacustrine ecosystem. The results reveal the earliest known complex lacustrine ecosystem after the EPME and suggest that Triassic lacustrine ecosystems took at most 10 m.y. to recover fully, which is consistent with the termination of the “coal gap” that signifies substantial restoration of peat-forming forests.
Abstract: As a more efficient quantitative method for morphological analysis, geometric morphometrics is applied to the flabellate fossils Flabellophyton including Flabellophyton lantianensis and Flabellophyton strigata from Neoproterozoic Ediacaran Lantian biota, South China. Both traditional morphometric analysis (including diverging angle, length, and width distribution) and geometric morphometric analysis [including superposition of normalized area analysis, non‐metric multidimensional scaling (n‐MDS), Bray‐Curtis similarity cluster analysis (CLUSTER) and analysis of similarities (ANOSIM)] were performed. The results indicate there are great interspecific morphological differences between F. lantianensis and F. strigata , in addition to some intraspecific variations within each species. Here we preliminarily suggest that the previously defined Flabellophyton should be subdivided into 2 genera at least: one marked by the dark transverse striated structure, and the other without. This recharacterization and reclassification work still needs further careful observation and comprehensive analysis with large number of flabellate fossils combining morphology, structure, population, and community‐ecology study.
The preservation of Ediacaran fossils in China are grouped into five preservational modes : phosphatization , kerogenization , pyritization , silicification and clay replication.Five representative fossil preservational modes identified in Ediacaran fossil Lagersttten in China and their tempo-spacial distribution patterns and taphonomic mechanisms are reviewed in this study.Our study indicates that kerogenization is the primary preservational style amongst the five taphonomic modes ; phosphatization and silicification are widespread ; and pyritization and clay replication are relatively rare in China.The kerogenization and pyritization are usually present in sandstones and mudstones ; while the phosphatization and silicification often occur in phosphorite , chert , and phosphatic and siliceous nodules.Several fossil preservational modes usually occur in the same fossil Lagersttte , resulting in multiple taphonomic pathways.Further integrated studies are required to test how the multi-preservational modes take place during the Ediacaran Period.
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