Geochemical characteristics of Eocene dolomite in the saline lacustrine basin, Qiadam, China

Abstract

By combining petrologic, structural and geochemical methods, the origins and characteristics of two sorts of lacustrine dolomite form are described and demonstrated in the Western Qaidam basin. The first lacustrine dolomite is the native biogenic algal dolomite, which is not abundant in the area. The analysis results of electron probe energy spectrum scan shows that the Mg element enrichment zone and the algal layer distribution are highly consistent, and have microbiological characteristics in the Western Qaidam basin, because microbial activity can overcome dynamics obstacles and have a favorable microenvironment for dolomite production. The second lacustrine dolomite is penecontemporaneous metasomatism micritic dolomite, which is widely distributed in the study area. Polarizing microscope and X-ray diffraction analysis reveal that most of the dolomicrite contain detrital grains and argillaceous components. This is because the mixed sedimentary detritus was brought from the periphery in the fan delta sediment. The electron microprobe analysis results 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, SiO2 and Al2O3 content is very rich, which clearly shows that dolomite belongs to penecontemporaneous metasomatic sediment. The results of this research have great significance for the carbonate exploration of oil and gas in the Qiadam basin.