Relationships between carbon isotope evolution and variation of microbes during the Permian–Triassic transition at Meishan Section, South China

Abstract

This paper investigates kerogen carbon isotopes, the difference between carbonate and kerogen carbon isotopes (D 13 C carb-kero = d 13 C carb -d 13 C kero ) and the difference between carbonate and n-C 19 alkane compound-specific carbon isotopes (D 13 C carb-n-C19 = d 13 C carb -d 13 C n-C19 ) during the Permian-Triassic transition at Meishan, South China. The results show that kerogen carbon isotopes underwent both gradual and sharp shifts in beds 23-25 and 26-29, respectively. The differences between carbonate and organic carbon isotopes, both the D 13 C carb-kero and D 13 C carb-n-C19 , which are mainly affected by CO 2 -fixing enzyme and pCO 2 , oscillated frequently during the Permian-Triassic transition. Both the variations of D 13 C carb-n-C19 and D 13 C carb-kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers. The episodic low values of D 13 C carb-n-C19 corresponded to episodic blooms of green sulfur bacteria, while the episodic high values of D 13 C carb-n-C19 corresponded to episodic blooms of cyanobacteria. The relationships between the variation of carbon isotopes and biota show that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly. Combining the carbon isotope compositions and the pattern of size variation of the conodont Neogondolella, this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous organic matters by sulfate reducing bacteria in the upper water column. Considered together with results from previous research, the high resolution variation of the biogeochemistry presents the sequence of the important geo-events during the PermianTriassic crisis.

Carbon cycle perturbation expressed in terrestrial Permian–Triassic boundary sections in South China

“…The reverse tricarboxylic acid (TCA) cycle that green sulfur bacteria use during the incorporation of carbon results in a smaller carbon isotope fractionation than the Calvin cycle that algal or cyanobacteria use (van Breugel et al, 2005). This hypothesis seems to be supported by the observed abundance of isorenieratane, a biomarker for green sulfur bacteria, at the event horizon in Meishan and Australia (Grice et al, 2005;Luo et al, 2010). Although, a rise in marine δ 13 C org values could also reflect greater productivity, lower pCO 2 , or shifting algal groups associated with the EPE.…”

A multistratigraphic approach to pinpoint the Permian-Triassic boundary in continental deposits: The Zechstein–Lower Buntsandstein transition in Germany

“…A further differentiation between phototrophic eukaryotic algae (including cyanobacteria) and sulfide-oxidizing bacteria ("green sulfur bacteria" according to Luo et al, 2010) may provide possible explanations for the respective shifts towards isotopically lighter δ 13 Corg values such as recorded here in the oolite horizon Alpha 1 (Calvörde Formation; Lower Buntsandstein Subgroup) in the Nelben section (Fig. 8).…”

How severe is the modern biotic crisis?—A comparison of global change and biotic crisis between Permian-Triassic transition and modern times

“…Silicolite gap means decimation of radiolarians, which may imply decline of phytoplankton on which they fed. When the macro-organisms became extinct, one of the main primary producers, cyanobacteria, flourished at first Xie et al, 2005), then wax and wane frequently during the PTB interval, and its flourish and decline reciprocally alternate with that of the SRB Luo et al, 2010). This phenomenon represented an instability situation of redox conditions in the global shallow water, and the latter severely shrank the base of marine ecosystem to the extent that there may be a global Fig.…”