Abstract: This paper is the first synthetical study on Permo-Triassic boundary(are calledPTB for short) of Tieshikou section in Xinfeng county, Jianxi Province, which is loccated in South China folded belt. It is based on the research of followingaspects: the biostratigraphy of conodonts, ammonites and bivalves; geochemical features of elements; oxygen and carbon isotope signature; sedimentary facies analysis and paleoenvironmental reconstruction; X-ray diffraction analysis of clay rocks around PTB; and grouping the ICP analysis data of rock samples collectedaround PTB by optimal division method. Through such synthetical studies, we determine the PTB of Tieshikou section at the base of No. 26 layer. The reasons arelisted as follows: 1. Faunas of Tieshikou formation (above and including No. 26 layer) include“Permiantype” and “Triassictype”forms, but faunas of Changxing formation(under No.26 layer)is “Permiantype” form. 2. Both the analysis of sedimentary facies and the geochemical features of elements indicate that No. 26 layer is the turning pointfrom wide carbonate platform environment to lagoon and shallow water seashore environment. 3. the JP26 clay rock from Tieshikou formation (No. 26 layer) is characterized mainly by both Illite and Kaolinite and a little Mixed Montmorillonite-Illite, the semiquantitative analysis shows the content of Illite, Kaolinite and Montmorillonite is 49%, 45% and 6%, respetively. In contrast to this, the main mineral of clay rocks from Changxing formation is Illite and with a little Chlo-rite, Kaolinite and Mixed Montmorillonite. Also by means of semiquantitative analysis, the content of Illite, Chlorite, Montmorillonite and Kaolinite is 80%， 8%， 7% and 5%, respectively. Thus No.26 layer is the difference limit line of clay rocks. The JP26 clay is a new type of PTB clay which is the first reported inthis paper. Besides this No. 26 layer is also the lithostratigraphic boundary. 4. The result of carbon isotope analysis indicate the values of carbon isotope changed obviously near the PTB. Strata under No. 26 layer all show positive valuesof δ¹³ C, but strata above No. 26 layer(including this layer)show negative values of δ¹³ C.The changing amplitude of δ¹⁸ O values under No.26 layer(5.4%)is larger than that of above No. 26 layer (0.64%).5. The ICP analysis of rock samples indicates that the trace elements fluctuated around the PTB at Tieshikou section. We have used the optimal division method to calculate these ICP analysis data. The No. 26 layer is the first important segement point.

Key words: Tieshikou section, PermoTriassic boundary, clay, synthetical study

摘要： 首次对江西信丰县铁石口二叠—三叠系界线剖面的生物地层学、岩石地层学、微量元素、碳及氧稳定同位素、粘土岩和沉积环境以及数学地质的有序最优分割计算进行了综合研究，通过分析，将铁石口剖面二叠—三叠系界线置于第26层底。界线粘土岩(第26层)的矿物组成以伊利石和高岭石为主，仅含少量蒙脱石伊利石不规则混层矿物，这是首次发现的新类型界线粘土岩。

关键词: 铁石口剖面, 二叠—三叠系界线, 界线粘土岩, 综合研究