北京石花洞第四纪钟乳石剖面的年代学研究

Chronology of a section of Quaternary speleothems in the Shihua cave, Beijing

北京石花洞位于房山花岗岩体边缘向形带的东北扬起端,与北京猿人遗址南北相望。地层为460Ma前形成的中奥陶统马家沟组石灰岩,洞穴大形态从25Ma前的上新世开始形成,洞内钟乳石从0.37Ma前的中更新世开始形成。在中国岩溶洞穴中,北京石花洞的层数最多,洞穴钟乳石种类齐全,裂隙渗透水沉积的石盾多、体积大,滴水沉积的石笋叠置关系明显,池水沉积的月奶石发育好,全新世石笋微层理发育清晰。该洞的大形态反映了北京西山新构造运动的期次,可以同华北地文期和永定河阶地对比,洞内钟乳石记录了中更新世以来北京西山古环境的变化,可以建立第四纪剖面,与周口店洞穴群碎屑沉积物剖面进行对比。钙板的铀系年龄为334.99～366.74ka,可定名钙板组。粗犷石笋的铀系年龄为169～235ka,粗犷石笋的电子自旋共振年龄为130～518ka,为中更新世沉积,可定名云水洞组。杆状石笋的铀系年龄为14.9±2.1～100.3±11.1ka,为晚更新世沉积,可定名石花洞组。在全新世石笋中,微层与微层之间存在厚约1μm的条带状纹线,是划分微层层数的标志,具有微层理的石笋14C年龄为为0.58～2.50ka,AMS14C年龄为为130±100～670±130a,可定名守备支洞组。

The Shihua cave is located at the northeastern end of the synformal belt at the edge of the Fangshan granite intrusion in Beijing and faces the Peking Man （Homo erectus pekinensis） site. The strata are composed of limestone of the Middle Ordovician Majiagou Formation formed 460 Ma ago. The basic form of the cave began to form in the pliocene at 25 Ma BP and the speleothems in the cave began to form in the middle Pleistocene at 0.37 Ma BP. Among Chinese karst caves, the Shihua cave has the largest number of Layers and a complete range of speleothems in the caves. There are many large cave stone shields deposited by fissure infiltration water, the superimposed relationship of stalagmites deposited by dripping water is evident, moonmilk deposited by pool water is well developed, and the micro-layering of Holocene stalagmites is clear. The basic form of the cave reflects the history of the neotectonic movement in the Westem Hills, Beijing, which may be correlated with the physiographic stage of North China and terraces of the Yongding RAver; the speleothems in the cave recorded the paleoenvironmental change in the Western Hills, Beijing, since the middle Pleistocene, which may be used to set up a Quaternary section for a correlation with the section of clastic sediments in the Zhoukoudian caves. The calcareous pLate has U-series ages of 334.99-366.74 ka, thus named the Gaiban Formation. The wide stalagmites have U-series ages of 169-235 ka and ESR ages of 130-518 ka, which are middle Pleistocene deposits and may be named the Yunshuidong Formation. The rod-shaped stalagmites have U-series ages of 14.9 ±2.1-100.3 ±11.1 ka, which are upper Pleistocene deposits, named the Shihuadong Formation. In Holocene stalagmites, there is usually a -1 μm thick, dark streak between two micro-layers, which serves as a mark for determining the number of micro-layers. Stalagmites with micro-layering have ^14C ages of 0.58-2.50 ka and AMS ^14C ages of 130±100-670±130 a, named the Shoubeizhidong Formation.