Validating the deep time carbonate carbon isotope records: effect of benthic flux on seafloor carbonate  

作　　者：Weiming Ding Ting Nie Yongbo Peng Yuanlin Sun Jinzhuang Xue Bing Shen 

机构地区：[1]Key Laboratory of Orogenic Belts and Crustal Evolution,MOE,School of Earth and Space Science,Peking University,Beijing 100871,China [2]School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

出　　处：《Acta Geochimica》2021年第3期271-286,共16页地球化学学报（英文）

基　　金：supported by the National Science Foundation of China(No.41772015 to Sun and No.41772359 to Shen)。

摘　　要：It is a consensus that marine carbonate archives the isotopic composition of seawater dissolved inorganic carbon(DIC,δ13Csw),the largest active C reservoir in the hydrosphere.Carbonate carbon isotope(δ13Ccarb)excursions have been used to reflect perturbations of the global carbon cycle and related environmental change.However,the deep timeδ13Ccarb records indicate faster and more pronounced perturbations of the carbon cycle compared to the present day.Here,we reportδ13Ccarb and elemental compositions of Late Paleozoic carbonate sections from South China,showing negative correlations betweenδ13-Ccarb and Fe^(2+)content of carbonate(Fecarb).We suggest that,because Late Paleozoic carbonate was mainly produced by benthic carbonate-secreting organisms,δ13Ccarbrecorded the isotopic composition near the seafloor,where benthic flux derived from anaerobic organic matter degradation delivers both Fe2+and 13C-depleted DIC from porewater.The binary mixing between seawater and benthic flux would result in the deviation ofδ13Ccarb fromδ13Csw.The negative correlation implies thatδ13Ccarb is influenced by benthic flux and is affected by the seafloor redox and sedimentation rate.The deep time spatially heterogeneous and temporally oscillatoryδ13Ccarb records in the basin-scale could be alternatively attributed to the variations of local environmental factors rather than aδ13Csw depth-gradient.Thus,the seafloor carbonate precipitation is continuously affected by diagenetic reactions in sediments,suggesting thatδ13Ccarb recording the seawater DIC composition is conditional.Our study urges that the interpretation ofδ13Ccarb should also consider the sedimentary process and depositional environment of marine carbonate.

关 键 词：Fe^(2+)content of carbonate(Fecarb) Benthic flux Sediment PALEOZOIC South China 

分 类 号：P736.21[天文地球—海洋地质]