The end-Permian mass extinction (EPME) occurred ～251.94 million years ago, was the most severe extinction event of the Phanerozoic, devastating both marine and terrestrial ecosystems, with the loss of ～81% and ～89% marine and terrestrial species, respectively.
Recently, the Late Paleozoic research group from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGAPS), Nanjing University and Yunnan University, have confirmed there were large-scale high-temperature wildfire combustion events through high-precision organic geochemical analysis of biomarker compounds polycyclic aromatic hydrocarbons, providing important insights into the collapse of terrestrial ecosystems and the changeover of vegetation during the Permian-Triassic (P-T) transition period.
The results were published on Earth and Planetary Science Letters.
Intensive volcanic activities around the Siberian Traps large igneous province and large-scale continental arc have triggered the massive release of greenhouse and poisonous gases, global warming, aridification and frequent wild？res. The abundance of PAHs, which can be important indicators for incomplete combustion of organic matter formed at higher temperatures because of wild？res, is a well-known alternative for investigating wild？re activities in geological history.
Most of the previous researches on PAHs focused onthe marine records during the P-T transition period, while the researches on the terrestrial records were relatively insufficient. Therefore, the study of PAHs in non-marine strata is of great significance to understand the history of wildfires.
The prehensive study on high-resolution PAHs in a non-marine P–T transitional sequence from the HK-1 drill core at the Lengqinggou section in Southwest China (Figs.1, 2). The PAHs content showed consistent significant enrichment during the P–T transitional period(Fig. 2), which was coupled with negative organic carbon isotope anomalies, revealing that there were large-scale high-temperature wildfire combustion events under the high-temperature and arid paleoclimate conditions during this period.
Additionally, low-molecular-weight compounds such as Dibenzofuran (DBF) were mainly derived from the biodegradation of terrestrial plant polysaccharides and lignin. "In the HK-1 drill core, the abnormally high concentration of DBF compounds and the co-variation with the combustion-derived PAHs indicate that the PAHs were mainly derived from high-temperature wildfire combustion of terrestrial plants and the tropical rainforest vegetation systems provided sufficient fuel for large-scale wildfires during P–T transition." says ZHANG.
ZHANG says, "furthermore, the low PAH contents in the Lower Triassic indicate a fuel shortage after the mass deforestation. The significantly changed PAH ratios indicated that the terrestrial ecosystem was greatly affected after the EPME." These PAH records suggested the vegetation type changed from a dense and highly diverse gigantopterid-dominated tropical rainforest ecosystem to an isoetalean-dominated herbaceous heathland-like ecosystem (Fig. 3).
This work is supported by the National Natural Science Foundation of China and the Strategic Priority Research Programs of the Chinese Academy of Sciences.
Reference: Jiao, S.L., Zhang, H.*, Cai, Y.F., Chen, J.B., Feng, Z., Shen, S.Z., 2023. Collapse of tropical rainforest ecosystems caused by high-temperature wildfires during the end-Permian mass extinction. Earth and Planetary Science Letters. 614, 118193. https://doi.org/10.1016/j.epsl.2023.118193.
Fig.1 GC–MS total ion chromatogram of Aromatic hydrocarbon fraction of HK-1 drill core sample in Southwest China, standard compounds, and sand blank sample.
Fig.2 Organic carbon isotope and selected PAH contents of HK-1 drill core in Southwest China.
Fig.3 Reconstructions of the terrestrial ecosystems during the P–T transition.
LIU Yun, Propagandist
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences
Nanjing, Jiangsu 210008, China