贵州紫云四大寨早三叠世地层初步研究

A PRELIMINARY STUDY ON THE LOWER TRIASSIC STRATA OFSIDAZHAI, ZIYUN, GUIZHOU PROVINCE

贵州紫云四大寨剖面下三叠统发育较齐全,化石较丰富。在此剖面上发现了大量牙形石、双壳类、菊石等生物化石,其中牙形石在该剖面上为首次发现,并识别出了早三叠世Neospathodusdieneri带、Neospathoduscrista-galli带、Neospathoduswaageni带和Neospathodushomeri-Neospathodustriangularis带的重要牙形石分子或带化石,可与国际同期地层中相应的牙形石化石带进行较好的对比;同时还发现了Claraiagriesbachi-C.concentrica组合和Claraiastachei-Claraiaaurita组合带的双壳类代表性分子。通过对这些化石综合分析,大致拟定了本剖面下三叠统格里斯巴赫亚阶(Griesbachian)、亭纳尔亚阶(Dienerian)、斯密斯亚阶(Smithian)和斯派斯亚阶(Spathian)的年代地层单位界线。

A well-developed Lower Triassic sequence in Sidazhai, Ziyun County, Guizhou Province is re ported here. Abundant fossils were collected from the Sidazhai Lower Triassic Section, including conodonts, bivalves, and ammonoids, among which conodonts were first reported at this section. Four conodont zones and two bivalve zones can be recognized in the section and are described in this paper. The four conodont zones in an ascending order are, the Neospathodus dieneri zone, Neospathodus cristagalli zone, Neospathodus waageni zone and Neospathodus homeri-Neospathodus triangularis zone. The two bivalve zones are the Claraia griesbachi-C, concentrica zone and Claraia stachei-Claraia aurita zone. According to the biostratigraphic zonations, the stratigraphic boundaries of the Lower Triassic Griesbachian, Dienerian, Smithians, and Spathian substages were established at the Sidazhai section.