Contributions to the Neoproterozoic Geobiology
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This thesis makes several contributions to improve our understanding of the Neoproterozoic Paleobiology. In chapter 1, a comprehensive quantitative analysis of the Ediacara fossils indicates that the oldest Ediacara assemblageâ the Avalon assemblageâ already encompassed the full range of Ediacara morphospace. A comparable morphospace range was occupied by the subsequent White Sea and Nama assemblages, although it was populated differently. In contrast, taxonomic richness increased in the White Sea assemblage and declined in the Nama assemblage. The Avalon morphospace expansion mirrors the Cambrian explosion, and both may reflect similar underlying mechanisms. Chapter 2 describes problematic macrofossils collected from the Neoproterozoic slate of the upper Zhengmuguan Formation in North China and sandstone of the Zhoujieshan Formation in Chaidam. Some of these fossils were previously interpreted as animal traces. Our study of these fossils recognizes four genera and five species. None of these taxa can be interpreted as animal traces. Instead, they are problematic body fossils of unresolved phylogenetic affinities. Chapter 3 reports stable isotopes of the Zhamoketi cap dolostone atop the Tereeken diamictite in the Quruqtagh area, eastern Chinese Tianshan. Our new data indicate that carbonate associated sulfate (CAS) abundance decreases rapidly in the basal cap dolostone and Î´34SCAS composition varies between +9â ° and +15â ° in the lower 2.5 m. In the overlying interval, CAS abundance remains low while Î´34SCAS rises ~5â ° and varies more widely between +10â ° and +21â °. Î´34Spy is typically greater than Î´34SCAS measured from the same samples. We propose that CAS and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin. Chapter 4 studies Î´13C, Î´18O, Î´34SCAS, and Î´34Spy of the Zhoujieshan cap carbonate that overlies the Ediacaran Hongtiegou glaciation. The Zhoujieshan cap dolostone shows positive Î´13C values (0 â 1.7â °). Î´34SCAS shows rapid stratigraphic variations from +13.9 to +24.1â °, probably due to relatively low oceanic sulfate concentrations. Î´34Spy shows a steady stratigraphic trend. Thus, the Î´34SCAS and Î´34Spy trends are decoupled from each other. The decoupling of Î´34SCAS and Î´34Spy trends suggests that CAS and pyrite were derived from different sulfur pools, which were probably due to the postglacial basin stratification.
- Doctoral Dissertations