9 / 2025-03-21 13:21:52

Lower–Middle Triassic conodont biostratigraphy and evolution from South Tibet, China, and implications for global correlations

Neotethys,Conodont,Permian-Triassic,Unitary Association Zone

Theme 3: Earth-Life Co-evolution Through Time > Session 3f: Rise of Modern-type Ecosystems in Triassic

The Permian–Triassic mass extinction was the most severe biotic crisis in the Phanerozoic, altering marine ecosystems from Paleozoic to Modern type (Sepkoski Jr., 1984; Erwin, 1994). Conodonts have played important roles in Triassic biochronology, providing a robust timescale for deciphering the mechanisms and patterns of mass extinction and aftermath recovery. Studies of Early–Middle Triassic conodonts in southern Tibet are relatively rare and lack high-resolution conodont biostratigraphies. In this study, three sections (Selong, Xialong and Gyanyima) from South Tibet have been extensively sampled bed by bed and studied to establish a high-resolution conodont biochronology.

The abundance of conodont individuals allows the recognition of 14 interval zones from Induan to Anisian in three sections in South Tibet, including two hindeodid zones and 12 gondolellid zones. The hindeodid zones are Hindeodus parvus Zone and Isarcicella staeschei Zone; the gondolellid zones are Clarkina taylorae Zone, Clarkina krystyni Zone, Neospathodus dieneri Zone, Neospathodus cristagalli Zone, Novispathodus waageni Zone, Scythogondolella milleri Zone, Novispathodus pingdingshanensis Zone, Columbitella elongatus Zone, Triassospathodus homeri Zone and Columbitella joanae Zone. Among them, two hindeodid zones are involved in Clarkina taylorae Zone; Columbitella elongatus Zone appeared simultaneously with Novispathodus pingdingshanensis Zone; and Triassospathodus homeri Zone is associated with Columbitella joanae Zone. In combination with previous work on southwestern Neotethys (SWN), 12 Unitary Association zones (UAZs), comprising three Griesbachian zones, two Dienerian zones, three Smithian zones, and four Spathian zones, were recognized, six of which were found in South Tibet.

Based on these new data from South Tibet, we have identified six stages in the evolution and diversification of the Early Triassic conodonts. Conodonts underwent fauna turnover in the late Griesbachian, while all Achignathodontidae went extinct. Gondolellidae recovered during the Dienerian–Smithian with increased richness of genera and species. A local decline in diversity occurred in the early Dienerian due to the extinction of Clarkina. A major extinction of conodonts occurred in the late Smithian. During the early–middle Spathian, conodonts experienced explosive radiation, and nearly all the Early Triassic conodonts died in the end-Spathian.