Biomarker evidence for biotic and environmental change across the Cambrian Series 2-Series 3 boundary at the Wuliu- Zengjiayan section, Guizhou, China

• Published in: Science China. Earth sciences 2014-11, Vol.57 (11), p.2781-2790
• Main Authors: Wang, ChunJiang, Zhao, YuanLong, Peng, Jin, Yang, XinLian, Bai, Jie, Liu, Yue, Chen, Tao
• Format: Article
• Language: English
• Subjects: Biota; Boundaries; Cambrian; Cyanobacteria; Earth and Environmental Science; Earth Sciences; Environmental changes; Geochemistry; Hydrocarbons; Kerogen; Phytoplankton; Research Paper; Sedimentary geology; 中国; 分子有机地球化学; 寒武纪; 海洋微生物; 环境变化; 生物标志物; 贵州省; 边界
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-014-4965-6

The Wuliu-Zengjiayan section in Jianhe County, Guizhou Province, China has been suggested as a potential Global Stratotype Section and Point （GSSP） for the defined base of Cambrian Series 3. A molecular organic geochemical study on the Cambrian Series 2-Series 3 boundary interval was carried out to reveal the biotic and environmental change during this transition. The hydrocarbons extracted from the Kaili Formation were proved to be indigenous. The various geochemical proxies such as biomarker parameter, δ13Corg, atomic H/C value of kerogen, and TOC content, co-vary along with the sedimentary column, and show a quick and significant change just across the Cambrian Series 2-Series 3 boundary. The less abundance of isoprenoid hydrocarbons, the relative enrichment of midchain monomethyl branched alkanes （mmb-alkanes）, the relatively negative value of δ13Corg, and the higher TOC contents may suggest that the upper Cambrian Series 2 was deposited in a relatively reducing environment with a higher organic input from cyanobacteria-predominated benthic microbial mats. On the other hand, the rela- tive enrichment of isoprenoid hydrocarbons, the less abundance of mmb-alkanes, the relatively positive value of δ13Corg, the lower TOC contents, and the lower atomic H/C values of kerogen are combined to indicate an enhanced phytoplankton pro- duction and an increased oxygen content and nutrients in the ocean during the early Cambrian Series 3, which could have benefited the explosion of the Kaili Biota. The Wuliu-Zengjiayan section may provide a typical case to understand the co-variation of marine microbe, animal, and environment.