Integrated Lithostratigraphy and Chemostratigraphy of the Ediacaran Doushantuo Formation, Yangtze Gorges, South China
Kathleen A. McFadden
Department of Geosciences Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061, USA
Late Neoproterozoic and Early Cambrian strata have proven to contain substantial oil reservoirs in Oman, Siberia, and China. In particular, black shales from the Ediacaran Doushantuo Formation (635-551 Ma) have been mined for coal and phosphatic ore, yet mechanisms for enhanced organic burial during this time in Earth history remains elusive. The termination of the Cryogenian glaciations (~750-635 Ma) potentially had significant impact on bioproductivity, basin-scale anoxia, and biological evolution during extreme fluctuations in global climate. However, high resolution studies have not been conducted on Neoproterozoic sections in China, resulting in considerable gaps with regard to regional and global correlation.Continuous deposition of two post-glacial black shale successions in the Doushantuo potentially record pulsed bioproductivity and/or enhanced preservation of organic carbon, evidenced by total organic carbon up to 4%, enhanced pyrite concentrations (up to 8 wt%) and positive carbon isotopic values (δ13Ccarb= +6‰) of interbedded carbonate in the lower shale. In contrast, the upper Doushantuo shale is lithologically comparable, yet are characterized by strongly negative carbon isotope values (δ13Ccarb= -10‰). Black shale deposition was likely long term (up to 50 Myr), yet dominant mechanisms are unconstrained. This study aims to address likely depositional mechanisms with integrated high-resolution lithostratigraphy and chemostratigraphy from the Yangtze Gorges area, South China. Refinement of the lithostratigraphic framework in China will provide critical climatic and depositional constraints during the terminal Neoproterozoic that will shed insight on the transition from extreme icehouse to greenhouse conditions and its relationship to organic carbon burial after glaciation.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid