重庆中梁山地区二叠—三叠系过渡层

THE PERMIAN-TRIASSIC TRANSITION BED IN THE MT.ZHONGLIANG AREA,CHONGQING

笔者通过重庆中梁山地区海相二叠—三叠系过渡层的发现及研究,认为二叠、三叠系原划定的假整合面不存在;过渡层的时代应定为早三叠世,也就是把前人厘定的二叠、三叠系界线上移1.01m。

The discovery of the marine Permian-Triassic transition bed in the Mt. Zhongliang area,Chongqing,has provided good conditions for the study of the Permian-Triassic boundary. Alternating sediments of six clayrock beds and six argillaceous limestone beds were discovered above the conventionally called Upper Permian Changxing limestone and at the base of the Lower Triassic Feixianguan shale.210 pieces of animal fossils were collected from the sequence.On identification,fossils in Nos.2—10 beds are all elements of the Late Permian Changxingian stage,e.g. Palaeofusma,Pseubophillipsia and Tetracorallia as well as large amount of brachiopods.Nos.11—14 beds are transition beds,yielding fossils such as Permian brachiopods Crurithyris and Orthotetina and Early Triassic bivalves Claraia, pteria ussurica variabilis and Eumorphotis.They form a mixed fauna. The mixture of the fossils shows that the stratigraphic section is successive. Considering that the appearance of new biotic elements is taken as the begin- ning of a new epoch,the authors propose that the Permian-Triassic boundary be placed at the base of the transition bed,i.e.the base of Bed No.11.