Characteristics And Genesis Of Dolomitic Zeolite Of Bayingebi Formation In Ingejing Depression Inner Mongolia

In this paper,the Lower Cretaceous Bayingebi Formation in Inge Depression of Bayingebi Basin in Inner Mongolia is taken as the research object.Through core logging and thin section analysis,X-ray diffraction,electron probe and scanning electron microscope of TZK-1 and TZK-2 wells,petrology and mineralogy analysis are carried out to classify lithology.Secondly,the origin of dolomitic zeolite in Ingejing Depression of Bayingebi Basin is analyzed based on the previous studies on the origin of analcite and other symbiotic minerals.Finally,the geochemical characteristics are analyzed through major trace elements,rare earth elements,carbon and oxygen isotopes,sulfur isotopes and strontium isotopes,the sedimentary environment,paleoclimate,tectonic environment and identification of material sources are analyzed through the content and ratio of relevant elements.Therefore,it is concluded that:(1)The lithology in Bayingebi Basin is relatively complex.According to mineral content,it is divided into mudstone,dolomite,analcite and mixed rock.Under the microscope,analcite has three forms:semi-automorphic,semi-automorphic and heteromorphic.The analcite occurrence has five types:striated layer,vein,crumpled bedding,"porphyry"and massive.(2)The average value of Ca/(Ca+Fe)of Bayingebi Formation in Inge Depression of Bayingobi Basin are 0.78.It shows that it was formed in the transitional environment from fresh water to salt water.Enrichment of light rare earth and loss of heavy rare earth;U/Th value greater than 1 is anaerobic environment;Ce has no anomaly,and Eu negative anomaly is mainly found in reductive environment.If Sr/Ba value is greater than 1,it means brackish water-saline water environment.Carbon isotope is mainly positive,Z average is 129.87,and oxygen isotope is mainly negative.The average temperature of lake water in Inge Depression is 51.37?,indicating that it is a low temperature"white smoke type"hydrothermal sedimentary rock from semi-salty lake to salty lake.(3)?³⁴S indicates a relatively closed sedimentary environment between-34.98and 24.93‰and the source of sulfur isotope is not single.Its genesis is both hydrothermal and biogenic.The average value of ⁸⁷Sr/⁸⁶Sr is 0.710314,and the source of hot fluid is the mixed hot fluid of crust and mantle.Therefore,analcite-bearing rocks are considered to be low temperature"white smoke type"hot water sedimentary rocks formed by the interaction between semi-salty lake-salty lake water and deep magmatic hydrothermal solution under drought partial reduction sedimentary environment.(4)Under the control of the Altyn Tagh fault,magmatism and the internal action of the hydrothermal solution in the lower part of the fault occurred to develop representative structural systems such as reticulate veins and laminae.The tectonic activity of the Altun fault zone provides the main channel for hydrothermal solution.