Two episodes of microbial change coupled with Permo/Triassic faunal mass extinction

Abstract

Microbial expansion following faunal mass extinctions in Earth history can be studied by petrographic examination of microbialites (microbial crusts) or well-preserved organic-walled microbes. However, where preservation is poor, quantification of microbial communities can be problematic. We have circumvented this problem by adopting a lipid biomarker-based approach to evaluate microbial community changes across the Permo/Triassic (P/Tr) boundary at Meishan in South China. We present here a biomarker stratigraphic record showing episodic microbial changes coupled with a high-resolution record of invertebrate mass extinction. Variation in the microbial community structure is characterized by the 2-methylhopane (2-MHP) index (a ratio of the abundance of cyanobacterial biomarkers to more general bacterial biomarkers). Two episodes of faunal mass extinction were each preceded by minima in the 2-MHP index, followed by strong maxima, likely reflecting microbial responses to the catastrophic events that caused the extinction and initiated ecosystem changes. Hence, both cyanobacterial biomarker and invertebrate fossil records provide evidence for two episodes of biotic crisis across the P/Tr boundary.

Triggers of Permo-Triassic boundary mass extinction in South China: The Siberian Traps or Paleo-Tethys ignimbrite flare-up?

“…Potential cause of the PTB mass extinction has been debated on (1) bolide impacts (Becker et al, 2010;Becker et al, 2004;Kaiho et al, 2006;Retallack and Jahren, 2008); (2) rapid anoxia in deep water (e.g., Twitchett, 1996, 2002); (3) a major sea-level fall or regression (Kozur, 2007); (4) large-scale continental flood volcanism (Campbell et al, 1992;Racki and Wignall, 2005;Renne et al, 1995) and (5) regional acidic volcanism of South China (Isozaki et al, 2007;Xie et al, 2010;Yin et al, 1989). The bolide impact model is not favored, given the absences of Ir anomaly, shock mineral assemblage and meteor crater around PTB sections in the world, and prolonged two-episode mass extinction pattern (Song et al, 2013;Xie et al, 2005;Yin et al, 2007Yin et al, , 2012. There are evidences for sea-level changes and super-anoxia across the PTB, but whether they are ultimate causes for mass extinction or by-product of large-scale volcanism (Isozaki et al, 2004) remains unclear.…”

“…Two-pulse or -stage patterns of the extinction were documented by a number of studies (e.g., Song et al, 2013;Xie et al, 2005Xie et al, , 2007Xie et al, 2010;Yin et al, 2007Yin et al, , 2012. The first pulse of extinction happened at MEH, and is denoted as the main extinction event or the Latest Permian mass extinction, which was marked by the extinction of 57% of species.…”

Geomicrobial functional groups: A window on the interaction between life and environments

“…Organic nitrogen isotope composition was clearly more negative in supratidal than in intertidal microbial mats, and heterocyst glycolipids, the biomarkers of some nitrogen-fixing cyanobacteria, were identified only in supratidal microbial mats [78]. The negative shifts of δ 15 N during Cretaceous oceanic anoxic events and across the PermianTriassic boundary both indicate past blooms of cyanobacteria [129,130], consistent with the occurrence of enhanced cyanobacterial biomarkers [131]. Nitrogen fixation needs more energy than nitrate-assimilating metabolism, and mi- N values also may be affected by microbial degradation of organic matter, terrestrial organic input and diagenesis.…”

“…Across the Paleocence-Eocence and Permian-Triassic boundaries, enhanced terrestrial weathering contributed more N, P and Fe to marine environments. The marine photosynthetic GFGs and diazotrophic GFGs flourished, and led to negative shifts of δ 15 N [130,131,174]. In most cases, the GFGs cannot only passively respond to nutrient change, but they also positively impact marine environments.…”

“…Thus, nutrient exchange in the water column can trigger a series of biogeochemical processes among different GFGs, which significantly affect marine environments. The presence of a variety of GFGs and the associated marine environmental changes across the Permo-Triassic boundary represented such a case in Earth history [130,131,165,174].…”