Geochemical Environment Restoration of the Lower Yangtze Paleocean in the Early Triassic,Southeastern China
ZUO Jing-xun1,3,TONG Jin-nan2,ZHAO Lai-shi1*,CHANG De-feng4,ZHAO Rong-jun3 1.State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China 2.State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences,Wuhan 430074,China 3.Henan Institute of Geological Survey,Zhengzhou 450001,China 4.Shandong Water Polytechnic,Rizhao 276826,China
Results of chemical analysis on rock samples collected from the north Pingdingshan Section,Chaohu,Anhui Province,Southeastern China,suggest that main elements of SiO2,Al2O3,Fe2O3,FeO,MgO,Na2O,K2O,TiO2,P2O5 and trace elements of Ba,V,Be,Nb,Zn,Cu,Ni,Co,Pb are rich in the Griesbachian,the Dienerian,as well as in the Smithian Subseries in the Lower Triassic.Eight distinct positive anomalies have been identified in the Lower Triassic on the basis of results of main and trace elements mentioned above.In ascending order,strength,size of anomalies and content of these elements in the Lower Triassic decrease gradually.In contrast to these elements,Sr and CaO are relatively concentrated in the Spathian subseries in the uppermost part of the Lower Triassic.Furthermore,trace element of Sr and main element of CaO enrich gradually up the north Pindingshan Section.Content of the former elements has negative correlation with δ13C values of carbonate,while the content of the later elements is positively related with δ13C values of carbonate.Commonly,δ13C value is used as an indicator of marine primary production and also used as an indicator to define restoration of marine ecological environment.Negative correlation between element contents and δ13C values indicates that the deteriorating marine environment is the tremendous disaster to the Early Triassic marine fauna in the Lower Yangtze region,while the positive correlation between element contents and δ13C values present that the feasible marine environment to the Early Triassic fauna.Eight marine geo-events have been identified in the Early Triassic based on the pronounced anomalies of trace elements and main elements.Strength of these events became weaker and weaker from the early Early Triassic to the late Early Triassic.A plenty of trace elements from the terrestrial volcano eruptions fluxed into the sea during the Late Permian and the Early Triassic,resulting in high content of argillaceous minerals and high grade of trace elements which led to paleocean environment deteriorating.Marine environment recovered as soon as the superfluous trace elements and argillaceous minerals deposited on the sea floor after volcano activities ceased.
【Fund】： 地质过程与矿产资源国家重点实验室开放课题(Nos.GPMR200903 MSFGGPMR201310);; 科技部基础性工作专项(No.2006FY120300-11);; 国家自然科学基金项目(Nos.40672023 41272025 40972003)
【CateGory Index】： P736.222
【CateGory Index】： P736.222