Responding Characteristics Between Ichnoassemblages And Paleo-Oxygenation Facies In Carbonate Rock Of The Taiyuan Formation In The Western North China Basin

The ichnofossils and ichnoassemblages of the Taiyuan Formation in the Jiaozuo area and Yuzhou area?western Henan province?,Fucheng area and Xishan area of Taiyuan city?middle south Shanxi province?have been carefully studied.The iron components and trace elements in the ichnofossils and their host rocks were tested and analyzed,and progress were made as follows:?1?The V,Co and Cu elements are not enriched in the Zoophycos with grayish-white fillings;V/Sc and V/?V+Cr?value all indicate the oxidizing environment.So,it is concluded that the Zoophycos with grayish-white filling formed in the oxidizing environment.The Co element is enriched in the Zoophycos with grey fillings;V/Sc and V/?V+Cr?value are close to the redox threshold.Therefore,it can be determined that the Zoophycos with gray filling formed in the weak oxidizing environment.The V and Co elements are enriched in the Zoophycos with red fillings;Fe_HR/Fe_T and V/Sc value indicate the reducing environment;V/?V+Cr?value indicates the weak reducing environment.it can be concluded that the Zoophycos with red filling formed in the weak reducing environment.The V element in the Zoophycos with black filling is significantly enriched;the Co and Cu elements are also enriched;V/Sc and V/?V+Cr?value indicate the reducing environment.Thus,it is explained that the Zoophycos with black fillings formed in the reducing environment.The Fe_HR/Fe_T value indicates anoxic environment in the burrow fillings of Nereites and Chondrites,it can be determined that these ichnofossils formed in the reducing environment.?2?Based on the analysis of the composition,occurrence,distribution characteristics of the ichnofossils and the sedimentary characteristics of their host rocks,and combined with the geochemical characteristics of the ichnofossils,four kinds ichnoassemblages of different paleo-oxygenation facies were established:Type A is Zoophycos with red fillings-Planolites ichnoassemblage,dysaerobic ichnoassemblage.It produced at the bottom of a relatively occluded bay lagoon.Type B is Zoophycos with grayish-white fillings-Skolithos ichnoassemblage,aerobic ichnoassemblage.It formed in an upper shallow sea or bay lagoon.Type C is Zoophycos with grey fillings-Helminthopsis ichnoassemblage,subaerobic ichnoassemblage.It occurred in the middle of a shallow sea.Type D is Nereites-Chondrites ichnoassemblage,anaerobic ichnoassemblage.It formed in the lower part of a shallow sea.