Characteristics Of Early Carboniferous Lithofacies-palaeogeography In Northeast China

Taking 11 outcrop profiles,21 observation profiles and 57 collected profiles in nort heast China as subject,this thesis sampled with outcrop profiles and that was 162 rock samples.Meantime,to the problems like confused stratum divisions and low research degrees of sedimentary environment,this thesis researched Early Carboniferous litho facies palaeogeography characteristics in northeast China through the analysis of characteristics of rock association and elemental geochemistry.The study area is in northeast China,and we identified 4 types of rock: clastic rock,carbonate rock and volcanoclastic rock.C lastic rock mainly was conglomerate,sandstone,siltstone,mudstone and shale;carbonate rock was sparite,micrite,grainstone a nd dolomite;volcanic rock mainly was basalt and andesite;volcanoclastic rock was mainly tuff.Structural patterns were mainly horizontal bedding,parallel bedding,lenticular bedding,cross-bedding and wavy bedding.Through analyzing elemental geochemistry characteristics of samples,we studied Early Carboniferous sedimentary environment.The result showed that major element has the characteristics of high Si,Fe and low P,Mn,K and Na,indicating that they have been influenced more by terrigenous sedime nt;minor element has the characteristics of high V,Li,Sr,Zr and low Be,Ta,Th,Hf,U;discriminant parameter like Sr/Ba,Th/U,V/C r,V/(V+N i)indicated that it was marine reduction environment;light rare earth element and heavy rare earth element differentiation were significant,while light rare earth element enriched;content of Ce was positive anomaly.Based on rock association,sedimentary and structural characteristics,as well as elemental geochemistry characteristics,we made research about sedimentary system in Early Carboniferous.4 kinds of sedimentary systems were identified,that was continental margin,neritic shelf,tableland and delta sedimentary system.And the subfacies developed were lagoon,backshore,foreshore,open-platform,restricted platform,delta front and fan delta.Combining the field survey profiles and regional strata data,we chose better profiles and counted layers' and sand-mud stone's thickness,and then compiled strata thickness map,mudstone thickness map,sandstone thickness map,mud comparison chart,sands comparison chart,and lithology comparison chart.and then made sure that it developed three provenance: north,south,and east.According to the principle of predominant rock facies and sedimentary facies,combining profiles analyzing,we made a research of Early Carboniferous lithofacies-palaeogeography characteristics.The result showed that the Early Carboniferous was mainly marine facies,and developed delta facies,carbonate platform facies and shallow marine facies.Among them,delta facies mainly developed central areas in Jilin and west part of the study area,and carbonate platform facies in northeast Neimenggu,and shallow marine facies developed widely.