山西云岗石窟侏罗系地震液化砂岩柱的发现及其大地构造意义
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本文为国家自然科学基金项目(编号:41772116)和中国地质科学院基本科研业务费项目(编号:YYWF201705) 联合资助的成果。


Discovery of the Jurassic seismic liquefaction sandstone pipes in the Yungang Grottoes, Shanxi province and its tectonic significance
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    摘要:

    本文主要报道在华北克拉通北缘云岗石窟景区内侏罗系地层中发现的20余个由地震液化形成的砂岩柱。地震导致的砂土液化是非常普遍的自然现象,地震波的震动使埋藏在地下未固结的饱和砂质沉积物迅速变为流体并在巨大压力下喷涌至地表,形成砂火山或泥火山。2008年汶川8. 0级大地震和2012年新西兰6. 2级地震都产生了严重的液化现象,在对地表造成严重破坏的同时,分别在地表形成了一系列的溢出丘和形态完好的砂火山。古地震之后,液化砂质沉积物往往在上涌的通道内固结成岩,形成穿层的岩柱或岩管。近年来,美国科罗拉多大峡谷相继发现很多地震液化形成的中生代巨型碎屑岩柱。2018年,本文作者在云岗石窟景区内的侏罗系云岗组中发现了20多条直径15~20cm左右、高可达2m以上穿层“侵入”的砂岩柱,有的在纵向上呈串珠状排列,有的呈不规则的树枝状自下向上伸展,膨大狭缩、分支复合现象非常明显,砂岩柱内部结构均一,不见任何层理。砂岩柱顶端的泥质围岩石中有明显向上牵引、拖拽的痕迹。这些砂岩柱没有任何硅化木的特征,也不是普通成岩作用形成的结核,与暴雨、泥石流、重力滑塌等作用均无任何关系,是古地震液化作用在地层内保存的遗迹,故称为液化砂岩柱。地震液化砂岩柱发育的层位位于李振宏等人(2014)在宁武—静乐盆地侏罗系云岗组顶部的凝灰质泥晶碳酸盐层位(160 Ma)之下约40m处,初步判定形成这些液化砂岩柱的古地震发生于160. 75 Ma~160 Ma之间的晚侏罗世。古地震的形成过程与燕山运动引起的地壳运动有直接的关联,是华北克拉通内与燕山运动伴生的古地震在地层中留下的最直接证据。

    Abstract:

    This paper mainly reports on the discovery of more than 20 earthquake- induced liquefaction sandstone pipes in the Jurassic strata in the Yungang Grottoes in the northern margin of the North China Craton. The liquefaction of sand caused by earthquakes is a very common natural phenomenon. The vibration of seismic waves causes the unconsolidated saturated sandy sediments buried in the ground to quickly become fluid and spew to the surface under great pressure to form sand volcanoes or mud volcanoes. In 2008, the Wenchuan M8. 0 Earthquake and the 2012 New Zealand M6.2 Earthquake caused severe liquefaction, forming a series of liquefaction mounds and well- shaped sand volcanoes on the surface. After the ancient earthquakes, liquefied sandy deposits often consolidate in the upwelling channel to form rock pillars or rock pipes, distributed through multiple strata. In recent years, hundreds of large Mesozoic earthquake- induced clastic pipes have been discovered in the Grand Canyon of the United States. In 2018, the authors disovered more than 20 similar meter- scale sandstone pipes with diameters of 15~20 cm and heights of more than 2 m in the Jurassic Yungang Formation in the Yungang Grottoes. Some pipes occur in a beaded shape in the longitudinal direction. Some pipes extend and stretch from bottom to top in irregular branches with distinct phenomena of expansion or contraction and branching or compounding. The internal structure of the sandstone pipe is uniform without any layering signs. Obvious traces of upward traction and dragging in the surrounding mudstones can be observed. These sandstone pipes, which show neither characteristics of silicified wood nor nodules formed by ordinary diagenesis, have no any relation to heavy rain, debris flow, or gravity collapse, but are the remains of earthquake- induced liquefication sandstones pipes which are preserved within strata. Earthquake- induced liquefication sandstones pipes occur mainly 40 m below the 160 Ma tuffaceous micritic carbonate at the top of Jurassic Yungang Formation in the Ningwu- Jingle Basin (Li et al. , 2014). It can be preliminarily concluded that the ancient earthquakes forming these liquefied sandstone pipes occurred in the Late Jurassic between 160.75 Ma and 160 Ma. Formation process of the ancient earthquakes was closely related to te crust movement caused by the Yanshanian movement. These sandstone pipes are the most direct evidence preserved in the strata by the ancient earthquake associated with the Yanshanian movement in the North China Craton.

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苏德辰,杨战兵,孙爱萍,乔秀夫.2019.山西云岗石窟侏罗系地震液化砂岩柱的发现及其大地构造意义[J].地质学报,93(8):1814-1830.
SU Dechen, YANG Zhanbing, SUN Aiping, QIAO Xiufu.2019. Discovery of the Jurassic seismic liquefaction sandstone pipes in the Yungang Grottoes, Shanxi province and its tectonic significance[J]. Acta Geologica Sinica,93(8):1814-1830.

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  • 收稿日期:2019-03-24
  • 最后修改日期:2019-04-22
  • 录用日期:2019-06-03
  • 在线发布日期: 2019-06-03
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