The relationship between dolomitization and organic matter occurrence in Lower Paleozoic carbonate in the Ordos Basin

Based on observations on the core and surface sections of Lower Paleozoic c arbonate in the Ordos Basin, petrography research and measurements of TOC, TOS, Ro, XRD, and comparative study with dolomite in modern Coorong Lake, i t has been revealed that: ( i ) dolomitization may occur in micrite limesto ne, gypsum-halite and argillaceous sandstone, and it can be divided into th ree types: sedimentary penecontemporaneous-early diagenesis, late diagenesi s of deep burial and catagenesis of uplift period. However, the crystal cel l of the second type less than 35 mu m in size is most closely associated w ith gas pool; (ii) the highest content of organic matter (OM) is produced i n samples from the argillic dolomite which may be formed by argillaceous fl uid through gypsum-halite; (iii) in the evolution process from penecontempo raneous dolomite into stoichiometric dolomite, the crystal order of dolomit e and the porosity of its host rock tend to increase, which is favorable to the formation of an available migration network. When the power of the flu id is high enough, the network is mainly favorable to the migration and tra nsport of heat, but when the power of the fluid goes down, the network syst em is favorable, due to its large space, to OM deposition in it.