Spatial-temporal Difference Of Geological Events During Permian-Triassic Crisis Interval: Lipid Molecules Records

The Permian-Triassic crisis event is considered as the biggest mass extinction in geological history,marking the end of the Paleozoic and the coming of the Mesozoic.But the direct killing mechanism remains controversial although there are all kinds of hypothesis about mechanisms of this biocrisis.Euxinia and global warming are widely accepted as tiggers for this biocrisis event.By studying spatial distribution characteristics of green sulfur bacteria and temporal distribution features of lipid molecules in Shangsi section,here we provide new ideas to euxinia hypothesis.At the same time,by analyzing spatial-temperal variation of wildfires and methane emissions,we provide new evidence for global warming.Aryl isoprenoids(AIs),biomarkers typical of obligate anaerobic green sulfur bacteria(Chlorobiaceae),were detected in 12 PermianTriassic boundary sections globally.Profiles of AI abundance from these study sections reveal significant spatio-temporal variation,documenting the development of photic-zone euxinia(PZE)before,during,and after the end-Permian mass extinction(EPME).No AIs were identified in the shallowest sections,but AIs are present in large amounts both prior to and following the mass extinction in 50-200 m sections and following the mass extinction in > 200 m sections,a pattern that is consistent with an oceanward expansion of PZE in the aftermath of the EPME.This expansion may have been fueled by an enhanced riverine nutrient flux as a result of global warming,terrestrial ecosystem destruction,and soil erosion,although intensified oceanic stratification as a function of climatic warming may have been a contributing factor.Marine euxinia is likely to have been a major player in the endPermian mass extinction.Generation of a long-term reservoir of euxinic waters at intermediate ocean depths would have created the potential for episodic shallowing of the chemocline or eruptions of sulfidic waters into the ocean-surface layer.A major event of this type may have caused a rapid kill-off of shallow-marine benthos during the end-Permian mass extinction,and episodic expansion of PZE following the EPME may have been a factor delaying the recovery of Early Triassic marine ecosystems.High methane index(MI),feature of high MI is GDGTs GDGT-1,-2 and-3 dominant,indicate there exist methane release events in marine environment.The earliest records of the archaea GDGTs were found in Jurassic.In this paper,we found the archaea GDGTs first appeared in the end-Permian and it has important meaning.Basis on GDGTs distribution in shallow water section Liangfengya and deep-water section Chaotian,no methane release evidence shown in Liangfengya section.During Clarkina changxingensis and Clarkina yini,high methane index indicate destabilization and dissociation of marine gas hydrates.High methane index also occur at the Early Triassic I.isarcica zone.Hence,the destabilization and dissociation of marine gas hydrates exist until the first biocrisis,may have been an contributing factors for temperature increase prior to the first mass extionction.However,Anaerobic methane oxidation is not the dominant process in the Latest Permian associated with the biggest carbon isotope negative excursion.The onset of gas hydrates dissociation lagged behind the onset of the second negative carbon isotope excursion,illustrating gas hydrates dissociation may not be an important reason for the second crisis,but an important factor in global warming at Early Triassic resulted in enhanced oceanic stratification and biotic slow recovery.Whether in geological history and the modern sediments,polycyclic aromatic hydrocarbons are considered to be the important evidence of wildfires.Based on the analysis of high molecular weight polycyclic aromatic hydrocarbons(PAHs)from three Permian-Triassic Marine section in south China,rapid increases in PAHs abundance prior to the first episode suggest terrestrial environmental deterioration occurring earlier than collapse of the marine ecosystem.Combining with coeval records of carbonate C-isotopes and volcanic activity,the first episode is regarded as an important trigger for the latest Permian extinction event in this study.In contrast to the first episode of wildfire,the second forest fire occurred at I.isarcica zone,synchronous with the second extinction.In conjunction with contemporaneous carbonate C-isotopes records and other geochemical parameters,hyperwarming is suggested as a trigger for the second episode of wildfire and marine crisis.In the process of interaction and co-evolution between organisms and environment,microbial functional groups play an indispensable role.In order to explore microbial functional groups on the response and feedback of the major environmental changes during the Permian-Triassic transition,we study the continuous sedimentary section,Shangsi section in Sichuan province.Using of organic geochemical analysis technology,especially the biomarkers and stable isotope technique,we analyzed and studied composition characteristics and evolution trend of microorganisms during Mid-Permian to Early Trassic.New lipid molecules evidence show the redox state of seawater and the wildfires change characteristics,illustrating the causal relationship between land and marine ecosystem destruction.The results show indicators of red algae and nitrogen-fixing bacteria increase during the first episode of the Permian-Triassic crisis.These indicators associated with evidence for enhanced wildfire and elevated soil erosion provides evidence for terrestrial events contributed to marine ecosystem collapse.In contrast,the second episode of the PTB mass extinction(ME2)was associated with expansions of green sulfur bacteria,nitrogen-fixing bacteria,and acritarchs coinciding with climatic hyperwarming,ocean stratification,and seawater acidification.Elevated temperature is believed to trigger for marine ecosystem changes during the second episode,which is different from the trigger for the first episode.Microbial records documented a much greater degree of marine environmental deterioration and collapse of the marine ecosystem structure during the second episode.