天津滨海地区G2孔磁性地层年代及其构造指示

    Magnetostratigraphy of drill hole G2 in the Tianjin coastal area and its tectonic significance

    • 摘要: 建立可靠的地层年代标尺对于研究滨海地区晚新生代沉积物记录的沉积环境变化、新构造运动及古气候演化具有重要意义。对位于天津滨海地区迄今所获得的最长的全取心钻孔G2(深1226m)进行了详细的磁性地层学研究,在此基础上探讨了该孔年代地层划分及其区域构造意义。结果表明,G2孔的底界年龄约为8.5Ma。其中,1226~658m为晚中新世,属馆陶组上部,658~303m属上新世明化镇组,303m以上属第四纪马棚口组、佟楼组、塘沽组和天津组,全新统天津组底界深度为19.4m。G2孔包含2个沉积速率较高(大于200m/Ma)的时期,分别为8.5~6.43Ma和3.58~3.03Ma。这2个时期与晚中新世以来青藏高原的扩展隆升在时间上有很好的可比性,指示高原隆升可能对华北地区的沉积和构造演化有重要影响。

       

      Abstract: It is of great importance to establish reliable chronologic framework in Binhai area for understanding the late Cenozoic depositional environment change, neotectonic movement and evolution history of paleoenvironment. In this paper, the authors present the magneto-stratigraphic investigation result in drill hole G2 (1226m), which is the longest drill hole in the Tianjin coastal area. On such a basis, the chronostratigraphic subdivision and its tectonic significance were also discussed. The results show that the core of this drill hole began deposition at about 8.5Ma BP. The strata of 1226~658m may be correlated to late Miocene and assigned to upper member of Guantao Formation, the strata of 658~303m belong to Pliocene Minghuazhen Formation, and the upper strata of more than 300m belong to Quaternary, including Mapengkou, Tonglou, Tanggu and Tianjin formations. The basal lower boundary of Holocene is identified at about 19.4m by 14C dating. Given the chronostratigraphic scale, two stages of relatively high sedimentation rate (>200m/Ma) can be revealed from drill hole G2, i.e., 8.5~6.43Ma and 3.58~3.03Ma, respectively. Both epochs have good comparability on the time scale with extension and uplift of the Tibetan Plateau. It is suggested that the uplift of plateau might also have had a significant impact on sedimentary and tectonic movement of the North China plain.

       

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