中国非海相二叠—三叠系界线层型剖面研究

吉木萨尔三台大龙口剖面已被推荐为国际非海相二叠─三叠系界线层型侯选剖面。该剖面是世界上研究非海相二叠─三叠系界线最理想的剖面之一，也是我国非海相二叠─三叠系界线研究程度最高的剖面。准噶尔南缘上二叠统─下三叠统统称仓房沟群，下分5个组（自下而上）：泉子街组、梧桐沟组、锅底坑组、韭菜园组、烧房沟组，除烧房沟组与下伏韭菜园组间有显著冲刷面外，各组间均为整合接触关系。仓房沟群中生物化石丰富，可以划分出植物、孢粉、双壳类、叶肢介、介形虫、脊椎动物等不同的生物组合，尤其重要的是在锅底坑组上部发育晚三叠世与早三叠世生物混生的过渡层。这个过渡层揭示了生物演变的连续性，即脊椎动物Jimusaria与Lystrosaurus共生，孢粉Lueckisporitesvirkkiae与Lundbladisporawatangensis共生，以及二叠纪型的植物、双壳、介形虫与三叠纪型的叶肢介之间的混生。即在这个过渡层中既含晚二叠世型的孑遗分子，也含早三叠世型的新生分子，因而可以确定二叠系与三叠系界线就在锅底坑组内，置于大龙口背斜南翼剖面第36层，北翼剖面第34层之底，即在锅底坑组与韭菜园组传统岩组界线之下约50m（北翼）～60m（南翼）处。古地磁反映的正负极性与生物地层界线基本一致。

STRATO-TYPE SECTION OF NON-MARINE PERMIANTRIASSIC BOUNDARY IN CHINA

Dalongkou section in Santai of Jimsar has already been recommended as a world-wide candidate of strato-type section of non-marine Permian-Triassic boundary. It is one of the most ideal setions in the world for studying non-marine Perimian-Triassic boundary, and also one to be studied to the highest in China.The Upper Permian-Lower Triassic of the southern margin of Junggar is called Banfanggou Group, including 5 formations, that is, from bottom up, Quanzijie Formation, Wutonggou Formation, Guodikeng Formation,Jiucaiyuan Formation and Shaofanggou Formation. They are in conformity contact with each other except that obvious scouring occurs between Shaofanggou Formation and underlying Jiucaiyuan Formation. Baofanggou Group yields abundant fossils, i. e., plants, sporo-pollen, bivalves, estheria,ostracoda and vertebrates.A transitional horizon with mixed biota of Late Permian and Early Triassic at the upper Guodikeng Formation is of great importance. It demonstrates succesive biological evolution, that is, association of Jimusaria and Lystrosaurus, that of Lueckisporites virkkiae and Lundbladispora watangensis , and mixing of Permian type plants, bivalves and estheria and Triassic type ostracoda. It so indicates that the transitional horizon yields not only late Permian remaining components but also early Triassic new components. Therefore the Permian-Triassic boundary is assured to be located in Guodikeng Formation, specifically at the 36th member of the southern limb section and the 34th member of the northern limb section of Daolongkou anticline, that is,about 50m (for northern limb) to 60m (for southern limb) under the boundary between Guodikeng Formation and Jiucaiyuan Formation. The paleomagnetic responds accord roughly with biological and stratigraphic boundaries.