Permian–Triassic Conodonts from Dajiang(Guizhou, South China) and Their Implication for the Age of Microbialite Deposition in the Aftermath of the End-Permian Mass Extinction

The widespread microbialites deposition that followed the End-Permian mass extinction in the Tethyan realm have been intensively studied because of the evidence they provide on the nature of this crisis and its aftermath. However, the age of the microbialite event remains controversial. New conodont collection across the Permian–Triassic（P–T） transition from Dajiang（Guizhou Province, South China） in this study enable us to discriminate four conodont zones, in ascending order, they are： Hindeodus parvus zone, Isarcicella lobata zone, Isarcicella isarcica zone and Hindeodus sosioensis zone. The age of microbialite in the P–T transition at the Dajiang Section is considered to be within the Hindeodus parvus zone and thus to clearly post-date the main extinction crisis. Reviewing the age of onset of microbialites throughout the Tethyan regions reveals two different ages： a Hindeodus changxingensis zone age is dominant in south-western and westernmost Tethys, whilst most other regions show microbialite deposition began in the Hindeodus parvus zone. Our investigation also indicates that two conodont changes occur at this time： an increase of hindeodid species immediately following a sequence boundary and the mass extinction, and a phase of extinction losses in the earliest Triassic Isarcicella isarcica zone during highstand development.

The Relationship between the “Green-Bean Rock” Layers and Conodont Chiosella timorensis and Implications on Defining the Early–Middle Triassic Boundary in the Nanpanjiang Basin, South China

The Triassic ＂Green-bean Rock＂ （GBR） layers were widely recognized around the Early-Middle Triassic boundary interval in the Nanpanjiang Basin, South China. To determine the precise relationship between the GBR layers and the first appearance datum （FAD） of the conodont Chiosella timorensis, four Lower-Middle Triassic sections from the Nanpanjiang Basin, including the Gaimao, Bianyang lI, Zuodeng and Wantou sections have been studied in detail. Detailed conodont biostratigraphy convinces us that there is no exact temporal relationship between the GBR layers and first occurrence of Ch. timorensis. Moreover, the numbers of the GBR layers are different from the place to place within the Nanpanjiang Basin, and the time span of the GBR layers was much longer than previously estimated. Global correlations show that the FAD of Ch. timorensis is contemporaneous basinwide and worldwide and more suitable marker defining the Olenekian-Anisian boundary （Early-Middle Triassic boundary） than any other proxies.