【摘要】 对准噶尔盆地南缘金沟河剖面进行了磁性地层学研究,建立了该剖面精细的磁极性年代框架,并探讨了准噶尔盆地南缘新生代地层的年代。金沟河剖面出露的新生代地层厚约4160m,由老到新依次为安集海河组、沙湾组、塔西河组、独山子组和西域组。通过系统热退磁和剩磁测量,1285块样品获得特征剩磁,并由此建立该剖面自出露的安集海河组底部至西域组中部厚约3250m地层的磁极性柱。根据该剖面极性柱的变化特征和剖面中发现的两处脊椎动物化石,与2004年标准磁极性柱进行了对比。结果表明,金沟河剖面研究段地层的年代约为28.0—4.0Ma,其中安集海河组、沙湾组、塔西河组和独山子组的年代分别约为28.0—23.3Ma、23.3—17.5Ma、17.5—13.2Ma和13.2—6.0Ma,根据沉积速率外推得到的西域组的年代约为6.0—1.1Ma。与前人划分的准噶尔盆地南缘新生代地层的年代相比较,金沟河剖面磁性地层学确定的安集海河组、沙湾组和塔西河组的年代与前人的划分基本相符,而独山子组和西域组的年代则明显偏老。更多还原

【Abstract】 A thick succession of the Cenozoic fluvial-lacustrine sediments was deposited on the southern margin of the Junggar Basin. This succusion preserves useful information to decipher the tectonic history of Tianshan Mountains and the environmental changes in the Junggar Basin. However, an accurate time scale of the Cenozoic strata has not been built. In order to construct a detailed time scale for the Cenozoic strata on the southern margin of Junggar Basin, we carried out a magnetostratigraphic study of the Jingou River section, which is located at the Huoerguosi Anticline, the westernmost one of the second fold and thrust fault zone in the northern piedmont of Tianshan Mountains. The new magnetostratigraphic data provide constraints on the ages of the different formations of the Cenozoic strata on the southern margin of Junggar Basin. The Jingou River section, about 4 160 m in thickness, is continuous according to the observed gradual change in sedimentary environments and can be divided into five formations: Anjihaihe, Shawan, Taxihe, Dushanzi and Xiyu in ascending order. Characteristic remanences (ChRMs) were isolated by progressive thermal demagnetization, generally between 300 and 680℃. A total of 1 285 samples yielded well-defined ChRMs and were used to establish the magnetostratigraphic column of a 3 270 m-thick section from the exposed base of the Anjihaihe Formation to the middle of the Xiyu Formation. Two vertebrate fossil horizons in the section and good correlation of the magnetostratigraphic column with the GPTS suggest that the section was deposited from ～28.0 to ～4.0 Ma. The ages of the Anjihaihe, Shawan, Taxihe, Dushanzi and Xiyu formations in the studied section are estimated to be ～28.0—23.3Ma, 23.3—17.5Ma, 17.5—13.2Ma, 13.2—6.0Ma and 6.0—1.1Ma, respectively. The ages of the Anjihaihe, Shawan and Taxihe formations are comparable to those published by previous researchers, whereas the ages of the Dushanzi and Xiyu formations are older than previously thought.更多还原