Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis

Abstract

International audienceOne of the most important carbon cycle perturbations following the end-Permian mass extinction event straddles the Smithian-Spathian boundary (SSB) (Olenekian, Early Triassic). This anomaly is characterized by a prominent positive carbon isotope excursion known from Tethyan marine rocks. Its global signifi cance is established here by a new high paleolatitude record (Spitsbergen). Paleontological evidence, such as Boreal palynological data (Barents Sea, Norway) and global patterns of ammonoid distribution, indicates a synchronous major change in terrestrial and marine ecosystems near the SSB. The reestablishment of highly diverse plant ecosystems, including the rise of woody gymnosperms and decline of the formerly dominating lycopods, is interpreted as an effect of a major climate change. This hypothesis is supported by modeling of ammonoid paleobiogeography, the distribution patterns of which are interpreted as a proxy for sea surface temperatures (SST). The latest Smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator SST gradient. In contrast, the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. We propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end-Smithian CO2 injection. The SSB event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end-Permian biotic crisis

Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions

“…The Spathian decline for the ammonoids has been recognized previously (11), as have all three Early Triassic declines for the conodonts (19). It seems never to have been generally recognized, however, that three major extinctions, entailing both taxa, occurred in the Early Triassic, and that these events must have been aspects of global mass extinctions for marine life in general.…”

“…Rather, as hypothesized previously (9)(10)(11)(12)25), mass extinctions were so frequent that most taxa were unable to recover markedly until the end of the epoch, and their losses in the three mass extinctions were also too light to have stood out in the fossil record. This appears to be true for common Early Triassic benthic taxa, such as bivalves, gastropods, and brachiopods, all of which are characterized by much lower characteristics of rates of diversification and extinction than ammonoids and conodonts (23).…”

“…1). The discovery of negative excursions in the Griesbachian, Smithian, and Spathian stages of the Early Triassic has led to the hypothesis that a succession of ecological crises similar to those of the Permian stifled recovery from the Permian crisis (9)(10)(11)(12). Thus, intervals between crises might have been quite hospitable to life but too brief to permit substantial diversification by most taxa.…”

High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Dienerian faunas of the Northern Indian Margin

“…When brought into a larger palaeogeographical perspective, it appears that anoxic events during the Early Triassic are concentrated in two main episodes coinciding with the lowest relative diversity and reduced morphological disparity of ammonoids: a middle to late Dienerian event and a late Smithian event (Galfetti et al, 2007c;Brosse et al, 2013;Bucher et al, 2013). Evidence for the middle to late Dienerian anoxic episode on outer shelves is found in the following well-dated, ammonoid-bearing areas: Nevada (Ware et al, 2011), South China (Galfetti et al, 2008) and southern Tibet .…”

Sedimentary evolution of the continental Early–Middle Triassic Cañizar Formation (Central Spain): Implications for life recovery after the Permian–Triassic crisis

“…During this latter period and even until the early Anisian, these excursions in the carbon isotope ratios have been related to climate variations (Kidder and Worsley, 2004;Galfetti et al, 2007b), paleo ceanographic changes (Atudorei and Baud, 1997;Briihwiler et al, 2009), rare and episodic sedimentation (Woods et al, 1999;Pruss et al, 2005) and even phosphate regeneration, productivity and re lated biodiversity (Payne and Krump, 2007).…”