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

A well-developed Lower Triassic sequence in Sidazhai, Ziyun County, Guizhou Province is reported here. Abundant fossils were collected from the Sidazhai Lower Triassic Section, including cono- donts, bivalves, and ammonoids, among which conodonts were first reported at this section. Four cono- dont 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.