--> Geochemical Characteristics of Eocene Dolomite in the Saline Lacustrine Basin, Qiadam, China

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Geochemical Characteristics of Eocene Dolomite in the Saline Lacustrine Basin, Qiadam, China

Abstract

Abstract

By combining petrologic, structural and geochemical methods, the origins and characteristics of two sorts of lacustrine dolomite from the Western Qaidam Basin are described and demonstrated. The first is the native biogenic algal dolomite, which is not abundant in the area. The analysis results of electron probe energy spectrum scan showed that the Mg element enrichment zone and the distribution of algal layer are highly consistent, and therefore its microbiological characteristics, because of that microbial activity, can overcome dynamics' obstacles and create a favorable microenvironment for the formation of dolomite. The second is penecontemporaneous metasomatism micritic dolomite, which is widely distributed in the study area. The results obtained through observations with a polarizing microscope and X-ray diffraction analysis revealed that most of the dolomicrite contain detrital grains and argillaceous components, which are due to the mixed piled of detritus brought from the periphery of the fan delta sediment. The results of electron microprobe analysis on the rock components demonstrated that the average content of FeO is 0.942% and that of MnO is 0.052%, which is significantly lower than that of hydrothermal dolomite. In addition, its SiO2 and Al2O3 content is also very rich, which clearly shows that it belongs to penecontemporaneous metasomatic sediment. The results of this research have great significance for the dense carbonate exploration of oil and gas in the Qiadam Basin.