The Analysis Of Dolomite Genesis Of Jixian System,Qishan Area

The problem of dolomite genesis is the most complex geological problem in carbonate rocks for hundreds of years.It has attracted a large number of geologists to study and established different genetic models for geologists with different origins of dolomite.So far there is no one genesis model that can solve all the problems of dolomite.The diagenetic fluid and diagenesis system in dolomite has been a hot topic of research.These problems are of great significance to the genesis of dolomite.Based on previous studies,this subject systematically studied the origins of dolomite in the Qishan area of Erdos Basin through methods such as thin sections of rock,trace elements,rare earth elements,carbon and oxygen isotopes,and Sr isotopes,and gained some conclusions:?1?According to the genesis-structure,there are four types of dolomite in the Qishan area.The geochemical characteristics of the trace elements indicate that the crystal dolomite is in a closed environment for a long time.It is the dolomitization of the marine fluid,and the caltice dolomite may be open.The depositional environment may into the atmospheric freshwater;?2?The analysis of rare earth elements shows that all types of rocks have similar distribution patterns,and the total amount of light rare earths is much greater than that of heavy rare earths,indicating that heavy rare earths in diagenetic fluids are more likely to be depleted and migrate;most of all dolomite types show Ce The negative anomalies indicate that they are in an oxidizing environment during sedimentation,while there is no obvious anomaly in Ce in caltice dolomite;whereas in Eu dolomite,there is one positive anomaly in the dolomite,and the others are negative ones;?3?Carbon and oxygen isotope data show that most of the sample data are more concentrated,indicating that the diagenetic fluids are similar in nature.The difference in?¹³C between individual samples may be related to weathering in the later diagenetic period,and the difference in?¹⁸O may be related to the depth of burial of rock;?4?Sr isotope analysis shows that the diagenetic environment of various rocks is relatively closed,and the Sr content of seawater in the same period is obviously higher than that of individual samples,indicating that the origin may be related to the deposition of siliceous rocks in the same period.In combination with the above mentioned knowledge of analysis and testing and petrology,the authors make a preliminary judgment on the genesis model of the dolomite in the Erdos Basin:Early dolomite was mainly marine sedimentation,and atmospheric freshwater was added at different stages of deposition.In the late period of deposition,it entered the buried dolomitization model.