10 research outputs found

    Palaeobiology of latest Ediacaran phosphorites from the upper Khesen Formation, Khuvsgul Group, northern Mongolia

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    Microfossil assemblages that include large acritarchs with complex processes, known as Doushantuo-Pertatataka-type acritarchs, are recovered from early Ediacaran successions globally. They are commonly found in shale and chert lithologies, but their diversity and palaeobiological significance is greatest when they are phosphatized. The best-known examples are from the Doushantuo Formation, South China, which preserves over 60 taxa including possible embryonic forms which may represent the oldest fossil animals. Fossils have only been recorded in four Ediacaran phosphorite deposits. Here we report the fifth such occurrence, from phosphorites of the upper Khesen Formation, Khuvsgul Group, northern Mongolia, where preservation rivals that in the Doushantuo Formation. The assemblage includes the likely cyanobacteria Obruchevella delicata, O. magna, O. parvissima and O. valdaica, as well as various Siphonophycus filaments, the possible alga Archaeophycus yunnanensis, and the Doushantuo-Pertatataka-type acritarchs Appendisphaera grandis, A. fragilis, A. tenuis, Cavaspina basiconica, Variomargosphaeridium gracile and V. aculeiparvum, sp. nov. The phosphorites also preserve the multicellular embryo-like taxon Megasphaera, which is represented by M. minuscula sp. nov. and potentially by M. puncticulosa. Geological and chemostratigraphical data suggest a latest Ediacaran age for the Khesen assemblage, immediately prior to the Proterozoic–Phanerozoic boundary. Thus, this is the youngest Doushantuo-Pertatataka-type microfossil assemblage yet described. It extends the range of Appendisphaera, Cavaspina, Megasphaera and Variomargosphaeridium upward by tens of millions of years. The assemblage adds to a growing database of Ediacaran fossils and emphasizes the importance of Mongolian strata to understanding the transition from a broadly microbial Proterozoic Eon to a Phanerozoic Eon where macroscopic animals acted as geobiological agents

    Microfossils in metasediments from Prins Karls Forland, western Svalbard

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    The stratigraphic importance of fossils is never more apparent than in attempts to unravel the complexities of metamorphic terrains. The age and stratigraphic relationships of the thick metasedimentary and metavolcanic succession of Prins Karls Forland, western Svalbard, have been the subject of investigation and debate since the early part of this century (Hoel 1914; Craig 1916; Tyrrel 1924), and sharply different interpretations have been proposed (e.g. Harland et al. 1979; Hjelle et al. 1979). Until now, such interpretations have been unconstrained by palaeontological data, an understandable consequence of the metamorphic alteration undergone by these rocks. In this paper, we report the discovery of stratigraphically useful microfossils preserved in chert nodules from carbonaceous, dolomitic shales on northern Prins Karls Forland. These fossils have significant implications for the stratigraphic and structural interpretation of Forland metasediments, as well as for the more general problem of palaeontological prospecting in severely deformed and metamorphosed terrains, including those characteristic of the Archean Eon
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