Abstract:Objectives: As a potential strategic reserve base for oil and gas exploration in the Qiangtang Basin, the discovery of the Longeni—Angdar Co paleoreservoir marked a new climax of the oil and gas exploration. The genesis of dolostone and its reservoir prediction are critical to the exploration of carbonate reservoirs in this case. However, the genesis of the saccharoidal dolostone reservoir has been under debate and attracted much attention. and there is no unified understanding of the genesis of dolostone in Buqu Formation in Qiangtang Basin, and the argument mainly focuses on the dolomitic fluid properties. This paper discusses the genesis of dolostone through geochemical characteristics and dolomitic fluid properties.Methods: In addition to the analysis of the temperature and salinity of the fluid inclusions, the values of carbon and oxygen isotope in fluid inclusions of Jurassic saccharoidal dolostone of Qiangtang Basin were calculated by the isotopic fractionation equation, and the dolomization fluid characteristics of the Jurassic saccharoidal dolostone in the Qiangtang Basin are discussed. Results: The temperature of the dolostone and limestone inclusions ranges from 50 to 220℃. The temperature of dolomite inclusions is significantly higher than that of calcite vein, and most samples are concentrated 150~220℃. In addition, compared with the limestone within the same layer, dolostone is more enriched in heavier carbon isotopes, which is a sign of high- temperature fluid—rock reaction. The carbon and oxygen isotopes of the dolomite inclusions were calculated by the carbon and oxygen isotopes fractionation equation, which were between -1.30‰~1.53‰ and 5.81‰~12.50‰ respectively, potentially results of high salinity brine.Conclusions: This study integrates comprehensive temperature, salinity and carbon—oxygen isotope analysis of inclusions, reveals that the saccharoidal dolostone of Buqu Formation in Qiangtang Basin is hydrothermal metasomatic origin.