北京平原区南部PGZ01孔第四纪地层划分及其环境意义*
Quaternary stratigraphic division and its environmental significance of Borehole PGZ01 in southern Beijing plain area

对北京平原区南部大兴榆垡镇420m 深的PGZ01孔岩心进行了岩石地层、磁性地层、¹⁴C测年、介形类组合和孢粉组合研究。结果表明:(1)Matuyama(松山)/Gauss(高斯)和Brunhes(布容)/Matuyama(松山)极性界线分别位于280m和78.35m处,钻孔底部已经进入Gauss正极性带;取280m处Matuyama/Gauss极性界线作为第四系下限,显示可能的永定河泥石流—冲积扇在第四纪之前即到达了北京平原南部,但是华北平原上新统标志岩石地层单元——厚层棕红色黏土在Olduvai(奥尔都维)极性亚带之上即已出现。(2)结合AMS¹⁴C测年,尝试将约60m以上地层的氧化—还原状况,与对古季风影响反映灵敏的沿海平原钻孔同样深度地层进行对比,继而确定上更新统和全新统的底界深度分别位于56.60m和18.95m。(3)MIS5(海洋同位素阶段)以来的特征沉积物,与沿海平原钻孔地层有很好的可比性,同时也有8~4ka期间史前大洪水的影响。本研究为廊(坊)固(安)凹陷西北边缘区第四纪地层划分对比、古地理环境演化、活动断裂以及区域差异构造沉降研究,提供了重要的年代地层格架,对理解晚更新世以来古季风变化的环境效应有重要的启迪。
Based on the core materials collected from the Borehole PGZ01,which is located at Yufa Township of Daxing district in southern Beijing plain area and has a depth of 420m,the analyses of lithostrotigraphy,magnetostratigraphy,AMS ¹⁴C dating,Ostracoda and sporopollen assemblages were carried out. The results show that: (1)The boundaries of Matuyama/Gauss polarity chron and Brunhes/Matuyama polarity chron appear at the depth of 280m and 78.35m, respectively. It suggests that the bottom strata of this borehole correspond to Gauss normal polarity zone at the bottom. Considering that the boundary of Matuyama/Gauss polarity chron at the depth of 280m is the lower boundary of Quaternary system. It suggests that the debris flow and alluvial fan or possible palaeo-Yongding River had arrived at the southern part of Beijing plain area before Quaternary. Moreover, thick-layer brownish red clay which is considered as the upper mark lithostratigraphic unit of the Pliocene occurred at the Olduvai subzone. (2)Integrated with the AMS ¹⁴C dating,the present study tentatively correlate the stratal oxidation-reduction status above the depth of 60m to correlate to cores from palaeomonsoonal-sensitive coastal plain environment,the boundary of the Upper Pleistocene and Holocene was determined to be at 56.60m and 18.95m, respectively. (3)The characteristic sediments deposited since MIS5 have a good correlation with core sediments from coastal plain environment,and show evidence of the influence of Prehistoric