Upper Norian conodonts from the Baoshan block, western Yunnan, southwestern China, and implications for conodont turnover.

The Sevatian of the late Norian is one of the key intervals in biotic turnover and in changes of paleoclimate and paleoenvironments. Conodont faunas recovered from two sections of upper Norian strata of the Dashuitang and Nanshuba formations near Baoshan City in western Yunnan province provide new insights into the diversity and biostratigraphy of the Sevatian conodonts within China as well as globally. A lower (.) Zone and an upper (.) Zone are identified in this area according to the first occurrences of and of . Rich conodont fauna of is detailed and presents various intraspecific forms. A total of 19 forms of P elements are presented, which, when combined with the reported conodonts in the Zone, suggest that there was a peak in conodont diversity within the Zone. A biotic crisis in the uppermost Zone is recognized from the contrast between the diverse conodont fauna in the Zone and the rare conodonts in the Zone. The conodont turnover during the middle Sevatian highlights the fact that the prolonged phases of the end-Triassic mass extinction probably began in the transition interval from Zone to Zone.