沉积学报2024，Vol.42Issue(3)：前插1-前插4,723-737,19.DOI:10.14027/j.issn.1000-0550.2023.107
弗拉—法门转折期气候—海洋环境变化及生物危机成因探讨
Paleoclimatic and Paleo-Oceanic Environment Evolution in the Frasnian-Famennian Transition:Potential causes of the biotic crisis
摘要
Abstract
[Objective]The Late Devonian Frasnian-Famennian(F-F)transition is a critical time interval in geologi-cal history.This period saw major simultaneous marine ecological system changes that led to one of the Big Five mass extinctions in the Phanerozoic.The F-F event(also referred to as the Kellwasser event)was characterized by severe losses of low-latitude shallow-water benthic faunas,notably reef-dwelling coral and stromatoporoids.High-latitude,deep-sea and terrestrial faunas were the least affected.Various separate or combined hypotheses have been proposed as the causes of this mass extinction(sea-level change,marine anoxia,climate change,volcanic/hydrothermal activi-ties,and bolide impact).Of these,climate change and marine anoxia have been the most intensively researched and discussed hypotheses based on the Web of Science in recent years.However,some controversies remain,and the in-teractions of certain factors are still unclear.[Methods]This study systematically reviews available reports on the pa-leoclimatic and paleo-oceanic changes during the F-F transition and discusses the anoxic model during this critical pe-riod,based on related case studies in southern China.[Results and Conclusions]Conodont oxygen and strontium isotopes,as well as the carbon isotope records for carbonates,collectively suggest a cold climate during the F-F tran-sition interval,with several rapid warming-cooling fluctuations.Conodont oxygen isotopes suggest that the sea-sur face temperature(SST)dropped by 5 °C-8 °C.Strontium isotopes also imply that the temperature fluctuations were due to frequent,short-duration volcanism.Palynological data and carbonate platform exposure/karstification are also suggestive of coeval climate cooling.Additionally,marine anoxia has been extensively hypothesized as a possible kill-ing mechanism in the F-F mass extinction,based initially on the presence of bituminous limestones(or black shales),named the lower and upper Kellwasser horizons.Studies of pyrite framboids,biomarker compounds,trace elements,isotopes of nitrogen,sulfur and uranium,and iron speciation have variously suggested the existence of the Kellwasser anoxic events.However,these generally occurred in geographically specific environments,notably in the pericontinental basins/sub-basins proximal to source hinterlands.Moreover,the range and degree of anoxia in the F-F transition also reportedly differed between study sections around the world.With regard to the anoxic model,studies have suggested that the Kellwasser anoxic events were caused by the increased nutrient input related to enhanced con-tinental weathering.Marine anoxic studies from three F-F sections comprising different depositional facies in southern China also support this"top down"anoxic model.Clearly,the F-F biotic crisis was not caused by any single factor.Frequent short-term volcanic activity may have enhanced continental weathering and associated greenhouse gas emis-sion,leading to frequent warming-cooling climate fluctuations and also increased oceanic nutrient input.In the latter case,eutrophication and anoxia would have occurred in shallow water,and the mutual interaction of the various envi-ronmental factors may have exerted biological pressure in the low-latitude shallow sea,and eventually led to the F-F biotic crisis.关键词
弗拉—法门转折期/古气候/古海洋氧化还原状态/生物危机Key words
Frasnian-Famennian transition/paleoclimate/paleo-oceanic redox condition/biotic crisis分类
天文与地球科学引用本文复制引用
张力钰,陈代钊,刘康..弗拉—法门转折期气候—海洋环境变化及生物危机成因探讨[J].沉积学报,2024,42(3):前插1-前插4,723-737,19.基金项目
国家自然科学基金项目(U19B6003,42330203)[Foundation:National Natural Science Foundation of China,No.U19B6003,42330203] （U19B6003,42330203）
