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10 results for “Organic-walled microfossils”
Data from: First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China
<p>Organic-walled microfossils offer an important window onto the biospheric evolution in pre-Cryogenian and provide biostratigraphic implications for many Proterozoic fossiliferous sequences which are poorly age constrained for the lack of reliable radiometric date. Recently, macroscopic carbonaceous compression fossils have been reported for the first time from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China. However, organic-walled microfossils have never been discovered in the Shiwangzhuang Formation before. To improve our knowledge about Proterozoic biodiversity in North China, we conducted a micropaleontological survey on the argillaceous limestone samples of the Shiwangzhuang Formation, which also contain macroscopic carbonaceous compression fossils, from the Baishicun section in Anqiu, Western Shandong, North China. Our investigation shows that the Shiwangzhuang microfossil assemblage is dominated by smooth-walled sphaeromorphic acritarchs and cyanobacterium-like filaments and relatively low abundance of other acritarchs, including 15 taxa, such as <i>Polysphaeroides filliformis</i>, <i>Ostiana</i> <i>microcystis</i>, <i>Simia annulare</i>, ?<i>Jacutianema </i>sp., <i>Pellicularia tenera</i>, <i>Polythrichoides lineatus</i>, and <i>Navifusa actinomorpha</i>. The Shiwangzhuang organic-walled microfossil assemblage, although consisting of long-ranging taxa and without age diagnostic taxa, is not contradictary with a Tonian age suggested by macroscopic carbonaceous compression fossils,<i> </i>including the <i>Chuaria</i>-<i>Tawuia </i>and <i>Sinosabellidites</i>-<i>Protoarenicola</i>-<i>Pararenicola </i>assemblages, revealed from the same horizon of the Shiwangzhuang Formation and organic-walled microfossil assemblage, including the late Mesoproterozoic to Tonian index fossils <i>Trachyhystrichosphaera aimika</i>, from the underlying Tongjiazhuang Formation. However, it is also worth noting that a Cryogenian or Ediacaran age cannot be completely excluded based just on the microfossils because of their limited biostratigraphic utility.</p>
Data from: First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China
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Diversity of organic-walled microfossils in the phosphates of the ca. 1 Ga Diabaig Formation, Torridon Group, NW Scotland
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Data from: Sustained shift in the morphology of organic-walled microfossils over the Ediacaran-Cambrian transition
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Data from: Affinity, life cycle, and intracellular complexity of organic-walled 2 microfossils from the Mesoproterozoic of Shanxi, China
Light microscope and scanning electron microscope observations on new material of unicellular microfossils Dictyosphaera macroreticulata and Shuiyousphaeridium macroreticulatum, from the Mesoproterozoic Ruyang Group in China, provide insights into the microorganisms' biological affinity, life cycle and cellular complexity. Gigantosphaeridium fibratum n. gen. et sp., is described and is one of the largest Mesoproterozoic microfossils recorded. Phenotypic characters of vesicle ornamentation and excystment structures, properties of resistance and cell wall structure in Dictyosphaera and Shuiyousphaeridium are all diagnostic of microalgal cysts. The wide size ranges of the various morphotypes indicate growth phases compatible with the development of reproductive cysts. Conspecific biologically, each morphotype represents an asexual (resting cyst) or sexual (zygotic cyst) stage in the life cycle, respectively. We reconstruct this hypothetical life cycle and infer that the organism demonstrates a reproductive strategy of alternation of heteromorphic generations. Similarly in Gigantosphaeridium, a metabolically expensive vesicle with processes suggests its protective role as a zygotic cyst. In combination with all these characters and from the resemblance to extant green algae, we propose the placement of these ancient microorganisms in the stem group of Chloroplastida (Viridiplantae). A cell wall composed of primary and secondary layers in Dictyosphaera and Shuiyouisphaeridium required a high cellular complexity for their synthesis and the presence of an endomembrane system and the Golgi apparatus. The plastid was also present, accepting the organism was photosynthetic. The biota reveals a high degree of morphological and cell structural complexity, and provides an insight into ongoing eukaryotic evolution and the development of complex life cycles with sexual reproduction by 1200 Ma.
Data from: Organic-walled microfossils from the Kistedalen Formation, Norway: acritarch chronostratigraphy of the Baltic Miaolingian and evolutionary trends of placoid acritarchs
<p>New acritarch data from the Kistedalen Formation based on two sections with continuous exposure allow to establish the most detailed Miaolingian acritarch biozonation in Baltica to date. Six interval zones previously established in Gondwana, the <em>Eliasum llaniscum, Cristallinium cambriense, Adara alea, Timofeevia lancarae, Cristallinium dubium</em> and <em>Vulcanisphaera turbata</em> zones, are identified, and their correlations within the Acado-Baltic Province examined. The diagnoses of <em>Retisphaeridium, Cristallinium, Retisphaeridium dichamerum, Retisphaeridium lechistanium, Cristallinium dubium</em> and <em>Cristallinium cambriense </em>are emended and the new species <em>Retisphaeridium rugulatum</em> sp. nov. and <em>Retisphaeridium minimum</em> sp. nov. are described. The diagnosis of R<em>etisphaeridium ovillense </em>(Cramer & Díez) Vanguestaine is emended and the species assigned to <em>Dictyotidium ovillense</em> comb. nov. The main evolutionary changes of the placoid acritarchs during the Miaolingian are analysed. Comparison with previous acritarch data from the Kistedalen Formation suggest that different extraction methodologies may result in significant bias in the recovered fossil record.</p>
Data from: Systematics of organic-walled microfossils from the ca. 780–740 Ma Chuar Group, Grand Canyon, Arizona
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Data from: Organic-walled microfossils of the mid-Neoproterozoic Alinya Formation, Officer Basin, Australia
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Data from: Affinity, life cycle, and intracellular complexity of organic-walled 2 microfossils from the Mesoproterozoic of Shanxi, China
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Data from: Organic-walled microfossils from the Kistedalen Formation, Norway: acritarch chronostratigraphy of the Baltic Miaolingian and evolutionary trends of placoid acritarchs
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