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A Review on the Global Palaeoproterozoic Positive δ~(13)C Excursion:Data Analysis and Matter Comment

GUAN Ping,WANG Yingjia The Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871  
Nearly all the literatures about Palaeoproterozoic positive δ13C excursion in the carbonate sequences on the earth during 2.20-2.06 Ga,which is called as Lomagundi Event,are reviewed.Hypotheses including biology evolvement,the rise of atmospheric oxygen,the Palaeoproterozoic ice age,super-continent break-up and evaporation,are proposed to interpret the Lomagundi Event in those literatures.Based on statistics of relations between the positive δ13C excursion and each geological phenomenon according to the data from those literatures,the authors conclude that those hypotheses are all reasonable,but different importance.The carbon isotope fractionation theory shows that the developing magnitude of buried organic matter will increase carbon isotope ratio of carbonate carbon reservoir.Biology evolvement can raise oxygen amount in atmosphere.Warm environment after the Palaeoproterozoic ice age and Kenorland super-continent break-up can both offer good conditions for biology developing.Thus,these evolutions can increase amount of buried organic matter and then cause positive carbon isotope excursion in carbonate carbon reservoir.Meanwhile,evaporation distributed over the world during the time may also cause positive δ13C excursion in local restricted environment,so the authors should research depositional environment case by case when considering the positive δ13C excursion.The authors analyzed original data of Mn/Sr,δ13C and δ18O from North America and Fennoscandian Shield to judge effect of weathering,diagenesis and metamorphism on carbon isotope data of the samples.The result shows δ13C and δ18O data of samples are reduced by weathering in some case.
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