A large epeiric methanogenic Bambuí sea in the core of Gondwana supercontinent?

作者：Sergio Caetano-Filho,Pierre Sansjofre,Magali Ader,Gustavo M.Paula-Santos,Cristian Guacaneme,Marly Babinski,Carolina Bedoya-Rueda,Matheus Kuchenbecker,Humberto L.S.Reis,Ricardo I.F.Trindade

摘要：Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through time,as long as they are acquired from waters where the dissolved inorganic carbon(DIC)is in isotope equilibrium with the atmospheric CO2.However,in shallow water platforms and epeiric settings,the influence of local to regional parameters on carbon cycling may lead to DIG isotope variations unrelated to the global carbon cycle.This may be especially true for the terminal Neoproterozoic,when Gondwana assembly isolated waters masses from the global ocean,and extreme positive and negative carbon isotope excursions are recorded,potentially decoupled from global signals.To improve our understanding on the type of information recorded by these excursions,we investigate the pairedδ^13Ccarb andδ^13Corg evolution for an increasingly restricted late Ediacaran-Cambrian foreland system in the West Gondwana interior:the basal Bambui Group.This succession represents a 1~(st)-order sedimentary sequence and records two majorδ^13Ccarb excursions in its two lowermost lower-rank sequences.The basal cap carbonate interval at the base of the first sequence,deposited when the basin was connected to the ocean,hosts antithetical negative and positive excursions forδ^13Ccarb andδ^13Corg,respectively,resulting inΔ^13C values lower than 25‰.From the top of the basal sequence upwards,an extremely positiveδ^13Ccarb excursion is coupled toδ^13Corg,reaching values of+14‰and-14‰,respectively.This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambui Group that occurs with only minor changes inΔ^13C values,suggesting change in the DIC isotope composition.We argue that this regional isotopic excursion is related to a disconnection between the intrabasinal and the global carbon cycles.This extreme carbon isotope excursion may have been a product of a disequilibria between the basin DIC and atmospheric CO2 induced by an active methanogenes

发文机构：Universidade de Sao Paulo MNHN Universite de Paris Universidade Estadual de Campinas Universidade Federal dos Vales do Jequitinhonha e Mucuri Universidade Federal de Ouro Preto Universidade de Sao Paulo

关键词：METHANOGENESISEDIACARANCAMBRIANCarbonisotopesSaoFranciscoBasinBambuiGroup

分类号： P59[天文地球—地球化学]