CHARACTERISTICS AND DISTRIBUTION OF SOURCE ROCKS OF THE SHUANGYANG FORMATION IN MOLIQING RIFT, YITONG BASIN

The Moliqing Rift is a second-order tectonic unit of the Yitong Basin. It has experienced four structural evolution stages, i.e. the tenso-shear stage, thermal subsidence stage, compresso-shear stage and compressional stage since Paleogene. The lacustrine muddy Shuangyang Formation is the main source rock of the rift. The organic matter, which is relatively high, mainly belongs to the typeⅡ₂, which is of humosapropelic transition, with the type Ⅱ₁ as the subordinate. The thickest mudstone of Shuangyang Formation occurs in the center of the rift, which thins from northwestern to southeastern. Aquatic organic matter dominates the source rock in the center, with terrestrial organic matter around the edge of the sag. The maturity of the organic matter in the Shuangyang Formation is relatively low. It is higher in the center of the sag, reaching the peak of the hydrocarbon generation while in the east and the south reaches only the threshold.