北京平原大兴区新-10孔研究及其地质意义

Study on xin-10 hole and its regional geological significance in Daxing District of Beijing Plain

《北京市多参数立体地质调查》项目施工的新-10孔,位于大兴区大红门小铺头村西,处于地质构造大兴隆起的上部,孔深145.87 m。揭露新生界埋深141.69 m,其中第四系埋深115.03 m,地层沉积特征差异性明显。通过对第四系与新近系(Q/N)界限附近(埋深100~129 m)岩芯精细描述,并选取49件孢粉含量较高的样品共同研究,结果表明该地区由新近纪时期孢粉组合主要为木本植物花粉的湿热环境逐步转变为第四纪孢粉组合以松为主的针叶林的干凉气候环境。结合钻孔上部地层共同分析得出,早更新世和中更新世沉积层很薄;永定河受气候与环境的共同影响,在晚更新世大兴地区多次泛滥形成冲洪积扇,寒冷的气候造成永定河冲洪积物加速沉积,将大兴隆起掩埋,形成了北京平原。

The xin-10 hole constructed by the project of Beijing Multi-Parameter 3D Geological Survey is located in the west of Xiaoputou village,Dahongmen,Daxing District,in the upper part of Daxing uplift,with a depth of 145.87 m.The burial depth of Cenozoic is 141.69 m,of which the burial depth of Quaternary is 115.03 m.The sedimentary difference is obvious.Based on the detailed description of the core near the Q/N boundary(100-129 m depth)and the study of the 49 samples selected with high sporopollen content,the results show that the humid and hot environment of Neogene sporopollen assemblage was mainly woody plant pollen,which gradually changed to the dry and cool climate of coniferous forest dominated by pine in Quaternary.Combined with the analysis of the upper strata of the borehole,it is concluded that the sedimentary layer of early Pleistocene and Middle Pleistocene is very thin.Influenced by the climate and environment,Yongding River inundated many times in Daxing area in the late Pleistocene to form the alluvial proluvial fan.The cold climate accelerated the deposition of the alluvial proluvial materials of the River,buried Daxing uplift and formed the Beijing plain.