The Early Triassic Biotic Recovery: a multiproxy approach

An improved resolution of the patterns and a better understanding of the processes involved in the Early Triassic recovery require acquisition both biotic and abiotic empirical data and testing of models by means of numerical simulations. A central prerequisite in this endeavor lies with (i): the construction of high-resolution and robust biochronological correlations allowing the assessment of diversity changes in time and space, and (ii): the calibration of such relative scales by means of high-resolution radiometric ages.

Appropriate evaluation of both regional and global diversity also heavily depends on what biochronological approach is utilized. The duration of the Early Triassic and the extremely uneven durations of its four substages have been newly established, as well as high-resolution correlations for the Smithian and Spathian low-paleolatitude ammonoids. Global changes in ammonoid diversity in time and space have been elucidated at the substage level and refined estimates at the zone level are under way. Their global trend bears a clear climatic signature as supported by our numerical geophyletic model.

The revised age control led to establish the global scope of the dramatic and abrupt fluctuations of the carbon cycle. Climatic changes as evidenced by palynofloras have also been demonstrated to be synchronous across paleolatitudes around the Smithian-Spathian boundary. The rest of the palynological record is under study. The Smithian-Spathian boundary has been shown to coincide with a major extinction of ammonoids and conodonts. Detailed analysis of pre-Smithian ammonoid diversity has just started. Efforts are newly devoted to integrate benthic organisms into the same time frame. Comparison of their diversity dynamics with that of ammonoids and conodonts hold great promises for unraveling which processes were involved during this time of protracted environmental instability.

Potential consequences of an extended eruptive activity of the Siberian traps appear as a reasonable hypothesis for this delayed recovery.