ON THE ORGANIC MATURITY OF THE ORDOVICIAN SYSTEM IN THE NORTHERN SECTION OF THE WESTERN MARGIN OF THE ORDOS BASIN BY USING CONODONT COLOR—ALTERED INDEX

In this paper,conodont color-altered index(CAI)is applied to the studies of the or-ganic maturity in the Ordovician system of the two structural units on the northern section of the western margin of the Ordors Basin.It is suggested that the value of CAI be 3 to 3.5 in the basin with paleogeotemperature of 115 to 140℃,and the evolutionary stage of organic matter can be attributed to mature to high-mature;while the value of CAI be 1.5 in the Tonggelagao fault block in overthrusting zone with a paleogeotemperature of 43℃,and the evolutionary stage of organic matter remains unmature.Moreover,the author of this paper questions the validity of the statement that the Tonggelagao fault block is formed by Yanshanian movement according to paleobiological and CAI reference.