印度阶-奥伦尼克阶界线层型候选剖面——安徽巢湖平顶山西剖面地层序列

A GSSP CANDIDATE OF THE INDUAN-OLENEKIAN BOUNDARY——STRATIGRAPHIC SEQUENCE OF THE WEST PINGDINGSHAN SECTION IN CHAOHU, ANHUI PROVINCE

位于安徽省中部巢湖市郊的平顶山西剖面被推荐为印度阶-奥伦尼克阶界线的全球层型候选剖面。系统记述了该剖面的地层序列,包括岩石地层、生物地层、磁性地层、碳氧同位素地层和旋回地层等方面的最新研究成果。该剖面包括3个岩石地层单元、7个牙形石带、5个菊石带、3个双壳类带;在剖面下段地层中识别出2个正向磁性带和2个反向磁极性带;与地球轨道天文周期相对应的Milankovitch气候沉积旋回也可以明确地辨认;碳氧同位素δ1 3Ccarb演变呈现两次大的旋回。以牙形石N eospathodus waageni首现定义的印度阶-奥伦尼克阶界线在该剖面上位于三叠系第二个主要的正向极性带近顶部,也接近三叠纪碳同位素δ1

The West Pingdingshan Section located in the suburb of the Chaohu City, Central Anhui Province, Southeast China has been proposed as the GSSP (Global Stratotype-Section and Point) candidate of the Induan-Olenekian boundary. This paper systematically describes the Lower Triassic stratigraphic sequence of the section and summarizes the up-to-date achievements in the lithostratigraphy, biostratigraphy, magnetostratigraphy, carbon and oxygen isotopes stratigraphy, and cyclostratigraphy. The strata in this section cover three lithostratigraphic units, seven conodont zones, five ammonoid zones and three bivalve zones. Two normal and two reversed magnetic polarity zones as well as the cyclic sequences corresponding to the Milankovitch climate periods driven by the Earth's orbit are well recognized in the lower part of the section. The δ 13 C carb excursion shows two big cycles from negative to positive anomalies throughout the section. The Induan-Olenekian boundary defined by the FAD of conodont Neospathodus waageni is located near the top of the second main normal magnetic polarity zone and the peak of the first Triassic positive shifting of δ 13 C carb at the section.