论二叠系-三叠系界线定义

<正> 一个合理的二叠系-三叠系界线定义对于正确划分它的界线和选择它的层型剖面是十分必要的。自1971年国际二叠系-三叠系界线会议(Calgary,Canada)以来,二叠系-三叠系界线研究有了很大的进展。在1984年莫斯科国际地质大会召开期间举行的二叠系-三叠系界线工作会议上,多数委员赞同以Otoceras 带的底为三叠系底界的传统定

On the definition of Permian-Triassic boundary

Represented by the base of Oioceras Zone, the traditional definition of Permian-Tria-ssic boundary is accepted by most of concerned scientists. Recent years, some scientists disagree with it, based on different recognition for Orioceras and conodonts representing the base of Triassic. 1. The cosmopolitan Otoceras being a typical Triassic ammonite genus with very short geological range is a reasonably leading fossil. The base of Otoceras zone lust symbolizes the mass extinction of Permian biota and ths beginning of flourish of Triassic biota, and also coincident basically with the boundaries of event stratigraphy. 2. Otoceras concavum is a species of typical Otoceras. Although it is similar to Julftoceras associated with Paratirolites in morphology, we should not therefore consider that the level of bearing Oto. concavum or the lower part of Oto. woodwardi is corresponding to the levels of bearing Paratirolites of Pseudotiroliies under none of stratigraphic evidences. 3. Currently, we have found Hindeodus parvus fristly from the base of Otoceras bed of Selo-ng Xishan section of southern Tibet. However, the base of Otoceras zone is coincident with the base of Hindcodes parvus zone. 4. Peribositra with short geological range, is common from the lower part of Otoceras zone of the Himalayan region and from the Hypophiceras bed, containing? Otoceras, of southern China. Thence, it is a better intermediary genus linking both regions of the Himalayas and southern China, and a good auxiliary fossil of traditional definition Permian-Triassic boundary also. 5. It is very dangerous that using a fossil "Association" (Anchignathodus parvus-Hypophiceras-Crurithysis speciosa-Towaptcria sc-ythica-Hollinellatingi "assemblage") is taken as a leading fossi: group of boundary definition. In fact, those elements compositing the "assocition" occurred from different biogeograp-hic regions, different biofacies areas with different bioenvrionments, and never from same horizon of same section. So, the "association" undoubtedly loses its affect of leading fossils of boundary definition.