FORMATION MECHANISM OF DISSOLUTION PORES IN THE MIDDLE AND DEEP LAYERS OF ORDOVICIAN IN TAHE AREA OF TARIM BASIN, CHINA

In order to clarify the characteristics and formation mechanism of the deep-sedimentary dissolution pores in in Ordovician of Tahe area, the field outcrop investigation, drilling core and micro-flake analysis were used to collect rock and cave and pore filling samples for oxygen and carbon strontium isotope and inclusion testing to restore porosity. Evolution history, identifying the source and properties of pore fluids. The study shows that the Lower Ordovician carbonate rocks in the Tahe area experienced normal shallow sea diagenetic environment, shallow surface freshwater diagenetic environment, early shallow burial diagenetic environment, uplifted exposed surface freshwater diagenetic environment, shallow-deep burial diagenetic environment Different diagenetic environments restrict the development and evolution of pores. The pores preserved today are mainly the unfilled intragranular dissolved pores and mold pores formed by the first stage of dissolution, and the intragranular dissolved pores formed by the fourth stage of dissolution. The dissolution pores are formed in the middle of the Caledonian II-III curtain or in the early Hercynian pressure-bearing environment, and belong to ascending karst. The crystal optics, oxygen and carbon isotope isotopes of calcite, uniform temperature, salinity and density of fluid inclusions, and cathodoluminescence analysis data support the filling fluid and the mixing of atmospheric fresh water and basin hot brine.