• 责任者：Zuo Jingxun (Nanjing Institute of Geology and Palaeontology ; Chinese Academy of Sciences ; Nanjing 210008 ; China)
• 刊名：Journal of China University of Geosciences
• 出版年：2008
• 卷期：19(1)
• 关键词：carbon isotope composition ; global seventh stage of Cambrian System ; Luoyixi Section ; northwestern Hunan
• 页码：p.
• 图表：5 illus., 1 table, 51 refs.
• issnNo：ISSN1002-0705
• isbnNo：CN42-1279/P

This work deals with the evolution of carbon isotope composition in the Luoyixi Section, a candidate of the Global Standard Stratotype-section and Point (GSSP), defining the base of  the   as-yet-undefined   seventh   stage   of   Cambrian   System   at   the   first   appearance   of   the   cosmopolitan agnostoid  Lejopyge     laevigata.  This  level  is  favored  in  a  vote  of  International  Subcommission   on Cambrian Stratigraphy (ISCS) as the biohorizon for defining the base of a global stage. Two hundred and sixty-four samples for carbon and oxygen isotope analysis have been collected from the carbonate successions at an interval of 0.25 to 0.5 m in this section. Results of the carbon isotope data exhibit a remarkable disciplinarian trend. The pattern of the carbon isotope evolution is gently undulant with a relatively   long   period   during   the   underlying   Drumian   Stage,   and   then   the   values   of  δ¹³C   fluctuate sharply   with   a   short   period   in  provisional   seventh   stage.   The   onset   of   sharp   fluctuation   in   the  δ¹³C values   begins   at   the   proposed   GSSP  level,   defining   the   base   of   the   global   seventh   stage,   where  δ¹³C values change from a gentle trend to a sharp trend. Distinct covariant-relationships among δ¹³C, δ¹⁸O, and sea level fluctuations suggest that a warming change in paleoclimate took place during the early global seventh stage, which led to a positive shift in δ¹³C values.