用磁性地层学方法讨论西域组的时代

通过对塔里木盆地及其周缘地区西域组砾岩的野外调查和磁性地层学研究，及相关层位的安山玄武岩同位素年龄测定等综合分析研究表明：西域组上段记录了松山负极性带下段， ２．５－１．６Ｍａ，上界大约位于奥尔都维正极性事件层位，年龄为１．６７－１．７６Ｍａ。上覆高阶地砾岩层及其下火山岩层年龄为１．４－１．６Ｍａ，西域组下段记录了高斯正极性

THE MAGNETOSTRATIGRAPHIC AGE OF THE XIYU FORMATION

According to field investigations and magnetostratigraphic studies of the Xiyu conglomerates of the Xiyu Formation and K-Ar age determination of andesitic basalt in a correlative horizon of the Xiyu conglomerates, it is shown that the upper member of the Xiyu Formation records the lower part of the Matuyama reversed epoch (M,2. 5-1. 6Ma) and that the upper age limit is defined at about the horizon of the Olduvai normal event (O,1. 67-1. 87Ma). The isotopic age of the volcanic rocks lying between the Xiyu conglomerates and the overlying conglomerate of the high terrace is 1. 4-1. 6Ma. The lower member of the Xiyu Formation records the Gauss normal epoch (G,3. 4-2. 5Ma). On the basis of the above studies combined with the stratigraphic contact relations, biostratigraphic study and characteristics of the tectonic deformation, the lower limit of the Quaternary in Tarim is temporarily defined at 1. 8Ma B. P. (which is consistent with the international opinion). Furthermore, the conglomerates of the upper and lower members of the Xiyu Formation are assigned to the upper and lower parts of the Upper Pliocene (N22x2 and N22x1) .respectively. The determination of the age of the Xiyu conglomerates and the stratigraphic correlation of the Quaternary of the Tarim basin may guide the oil-gas exploration of Tarim,so have certain practical significance.