Smithian-Spathian Boundary: The Biggest Crisis in Triassic Conodont History

Ongoing work in California, S-China, Tibet, Pakistan and Oman has led to a refined biochronologic subdivision of the late Early Triassic and allows reconstructing a high resolution diversity time series, partly constrained by new U-Pb ages from S-China [1-2].

Conodonts crossed the PTB without major changes [3]. In the Early Triassic the first major conodont faunal turnover occurred during the late Griesbachian - early Dienerian, with the disappearance of Anchignathodontids (Hindeodus-Isarcicella group), which were replaced by the emergent Neospathodus and Borinella? species.

In the earliest Smithian, conodonts experienced a dramatic radiation, which ended in a major extinction during the late Smithian. This extinction was the most severe of the entire Triassic in terms of generic diversity and multi-element apparatuses. In the early Spathian conodonts radiated again explosively and gradually declined during late Spathian times.

These global diversity patterns coincide with large perturbations of the global carbon cycle [4-7]. As indicated by changes in the latitudinal gradient of generic richness of ammonoids [8], the boreal palynological record [6], and a prominent positive δ¹³C-isotope shift, the late Smithian - early Spathian boundary interval is marked by a severe climatic change.

[1] Galfetti, T. et al. 2007a: EPSL 258.

[2] Ovtcharova, M. et al. 2006: EPSL 243.

[3] Orchard, M. 2007: PPP 252.

[4] Brühwiler, T. et al. 2007b: SGM Geneva.

[5] Galfetti, T. et al. 2007b: PPP 243.

[6] Galfetti, T. et al. 2007c: Geology 35.

[7] Payne, J. et al. 2004: Science 5683.

[8] Brayard, A. et al. 2006: PPP 239.