|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China, and Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2 Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154, USA
3 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
4 Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
5 Department of Earth Sciences, University of California, Riverside, California 92521, USA
6 Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA
Two distinctive volcanic ash beds were found in the terminal Proterozoic Doushantuo Formation in south China. The lower ash bed, 
2.5 m above the cap carbonate at the base of the Doushantuo, yields a U-Pb zircon age of 621 ± 7 Ma, providing the closest upper limit for a correlative of the Marinoan glaciation. The upper ash bed, near the Doushantuo-Dengying boundary, yields a U-Pb zircon age of 555.2 ± 6.1 Ma, providing for the first time a direct age determination for a prominent negative 
13C excursion (
–5
) above the Marinoan glacial level. This excursion, if interpreted to be of glacial origin, is much younger than the Gaskiers Formation (ca. 580 Ma) in Newfoundland, and perhaps the fifth or sixth such level in the Neoproterozoic. That interpretation, however, is not supported by the proliferation of organisms within strata encompassing the negative 13C excursion in south China and globally, by the lack of a ca. 555 Ma glacial record, and by the absence of stratigraphic evidence for sea-level change. The data call for alternative paleoceanographic models for the origin of Neoproterozoic 13C excursions not clearly related to glaciation.
Key Words: U-Pb • SHRIMP geochronology • Neoproterozoic glaciation • cap carbonates • south China
This article has been cited by other articles:
|
|
 |
|
  S. A. Bowring, J. P. Grotzinger, D. J. Condon, J. Ramezani, and M. J. Newall Reply to comment: Oman Chronostratigraphy: (Reply to comment by Erwan Le Guerroue, Ruben Rieu and Andrea Cozzi on "Geochronologic Constraints on the Chronostratigraphic Framework of the Neoproterozoic Huqf Supergroup, Sultanate of Oman", American Journal of Science, v. 307, p. 1097-1145) Am J Sci, January 1, 2009; 309(1): 91 - 96. [Full Text] [PDF]
|
|
|
|
 |
|
 W. ZHU, Z. ZHANG, L. SHU, H. LU, J. SU, and W. YANG SHRIMP U-Pb zircon geochronology of Neoproterozoic Korla mafic dykes in the northern Tarim Block, NW China: implications for the long-lasting breakup process of Rodinia Journal of the Geological Society, September 1, 2008; 165(5): 887 - 890. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Liu, S. Gao, C. Diwu, and W. Ling Precambrian crustal growth of Yangtze Craton as revealed by detrital zircon studies Am J Sci, April 1, 2008; 308(4): 421 - 468. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. F. Zheng, B. Gong, Z. F. Zhao, Y. B. Wu, and F. K. Chen Zircon U-Pb age and o isotope evidence for neoproterozoic low-18O magmatism during supercontinental rifting in South China: Implications for the snowball earth event Am J Sci, April 1, 2008; 308(4): 484 - 516. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Jiang, M. J. Kennedy, N. Christie-Blick, H. Wu, and S. Zhang Stratigraphy, Sedimentary Structures, and Textures of the Late Neoproterozoic Doushantuo Cap Carbonate in South China Journal of Sedimentary Research, July 1, 2006; 76(7): 978 - 995. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. J. Peterson and N. J. Butterfield From The Cover: Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record PNAS, July 5, 2005; 102(27): 9547 - 9552. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
