安徽巢湖地区下三叠统综合层序

An Integrated Lower Triassic Sequence in Chaohu, Anhui Province

印度阶 -奥伦尼克阶界线的全球层型候选剖面之一位于安徽巢湖地区 ;巢湖地区的下三叠统也是国际上同期地层中生物地层序列最有代表性、多重地层学手段应用齐备、研究效果最好的地层序列之一 .根据巢湖地区 3条代表性下三叠统剖面的岩石地层、生物地层和碳同位素地层的最新研究成果归纳出本区早三叠世综合地层序列 ,作为区域地层对比研究的标准 .巢湖的下三叠统明确包含 8个牙形石带和 6个菊石带 ,它们具有区域甚至全球对比意义 ;巢湖地区早三叠世碳同位素δ1 3 Ccarb的演变呈现 2个显著的漂移周期 ,这种有特色的碳同位素漂移 ,不仅具有地层学价值 ,而且可能对于三叠纪初的生物复苏和生态系演变具有指导意义 .在综合地层序列基础上 ,将 3条剖面的古地磁学研究成果链接 ,形成了巢湖地区完整的早三叠世磁性地层序列 ,包括 5个主要的正向极性带和 5个反向极性带 ,这也是目前在本区乃至华南获得的最完整的早三叠世磁极性序列之一 .

One of the GSSP (Global Stratotype Section and Point) candidates for the Induan-Olenekian boundary is situated in Chaohu, central Anhui Province, southeast China. Chaohu also has a representative and well-expressed Lower Triassic sequence that has been better studied in various aspects. This paper presents an integrated and comprehensive Lower Triassic sequence of Chaohu to serve for a standard regional stratigraphical sequence, based upon up-to-date achievements in the (studies) of lithostratigraphy, biostratigraphy and carbon isotope stratigraphy at three sections in the area. Eight conodont zones and six ammonoid zones are consequently well distinguished in the Lower Triassic of Chaohu, and most of them are (regionally) or even globally correlative. The δ^(13)C_(carb) excursion shows two characteristic shifting periods, and this carbon isotope sequence is not only of a stratigraphic value but also of great importance to understanding the biotic recovery and ecosystem reconstruction at the beginning of the Triassic. In the light of the integrated Lower Triassic sequence, a complete Lower Triassic magnetic stratigraphic sequence is established from the data at the three sections. The Lower Triassic covers five major normal polarity zones and five reversed polarity zones, and both the Permian-Triassic boundary and the Induan-Olenekian boundary are located inside normal polarity zones.