GENESIS OF ORDOVICIAN MATRIX-POROSITY DOLOMITE RESERVOIR IN THE TARIM BASIN

There is a large quantity of deeply buried dolomite with well-developed matrix porosity in the Lower Ordovician of the Tarim Basin which can be quality reservoir.The development of this kind of dolomite is facies-controlled and the initial rock is grainstone of grain bank facies,according to the analyses of cores,thin sections and cathodeluminescence.The dolomite formed under burial condition which is the product of burial dolomitization,based on the study of petrology,trace element,degree of order and homogenization temperature of the dolomite.It is predicted from the trace element,rare earth element and Sr isotope that the dolomitizing fluid is modified seawater which may be related to Mg²⁺-bearing seawater in Cambrian evaporative platform.Permian volcanic activity is supposed to be the driving force of dolomitization over the entire platform and the burial dolomite in the Lower Ordovician formed by means of the replacement of overlying limestone by underlying Mg²⁺-bearing seawater in Cambrian evaporative platform through thermal convection.