Title page for ETD etd-12072007-104326


Type of Document Dissertation
Author Shen, Bing
Author's Email Address bingshen@vt.edu
URN etd-12072007-104326
Title Contributions to the Neoproterozoic Geobiology
Degree PhD
Department Geosciences
Advisory Committee
Advisor Name Title
Xiao, Shuhai Committee Chair
Bodnar, Robert J. Committee Member
Kowalewski, Michal Committee Member
Read, James Fredrick Committee Member
Keywords
  • Neoproterozoic
  • Ediacaran
  • Ediacara fossils
  • China
  • Carbon isotope
  • Sulfur isotope
  • Disparity
Date of Defense 2007-11-29
Availability unrestricted
Abstract
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 assemblage—the Avalon assemblage—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 δ34SCAS composition varies between +9‰ and +15‰ in the lower 2.5 m. In the overlying interval, CAS abundance remains low while δ34SCAS rises ~5‰ and varies more widely between +10‰ and +21‰. δ34Spy is typically greater than δ34SCAS 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 δ13C, δ18O, δ34SCAS, and δ34Spy of the Zhoujieshan cap carbonate that overlies the Ediacaran Hongtiegou glaciation. The Zhoujieshan cap dolostone shows positive δ13C values (0 –1.7‰). δ34SCAS shows rapid stratigraphic variations from +13.9 to +24.1‰, probably due to relatively low oceanic sulfate concentrations. δ34Spy shows a steady stratigraphic trend. Thus, the δ34SCAS and δ34Spy trends are decoupled from each other. The decoupling of δ34SCAS and δ34Spy trends suggests that CAS and pyrite were derived from different sulfur pools, which were probably due to the postglacial basin stratification.

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