下三叠统殷坑阶和巢湖阶及其界线研究

STUDY ON THE LOWER TRIASSIC YINKENGIAN AND CHAOHUAN STAGES AND THEIR BOUNDARY

系统介绍层型剖面殷坑阶和巢湖阶的定义和地层特征,并重点讨论了两阶之间的界线,即巢湖阶的底界。巢湖阶的底界层型位于近期提出的全球印度阶?奥伦尼克阶界线层型候选剖面———安徽巢湖平顶山西坡剖面上,界线定义为以牙形石Neospathodus waageni的首现点作为第一标志,菊石Flemingites-Euflemingites带底界作为参考标志。在巢湖剖面上,该界线位于三叠纪第2个正向磁极性带上部、三叠纪碳同位素曲线第1次正向漂移峰值附近;在岩石地层系统中,它位于殷坑组中上部位。简要概述了该界线地层的国际和国内对比的主要标志性化石。

The China National Stratigraphical Commission proposed that the marine Lower Triassic of China is chronostratigraphically divided into two stages. Yinkengian and Chaohuan. This paper introduces the definitions and stratigraphical sequences of the Yinkeng and Chaohuan Stages in the type sections and focuses on the boundary between the stages, i.e. the base of the Chaohuan Stage, which is defined in the candidate stratotype section of the global Induan-Olenekian boundary, i.e. the West Pingdingshan Section in Chaohu, Anhui Province （Tong Jin-nan et al. , 2003）. The boundary is first defined by the FAD of conodont Neospathodus waageni, and the base of ammonoid Flemingites-Euflemingites zone is the reference. In the Chaohu section this boundary is situated in the upper part of the second Triassic normal magnetostratigraphical polarity zone and close to the first Triassic positive peak in the carbonate carbon isotope excursion. In lithostratigraphy the boundary is located in the middle-upper part of the Yinkeng Formation. In addition, the paper briefs the major index fossils for the correlation the boundary strata throughout southern China and globally.