华北克拉通中-新元古代古地震记录及多期裂解事件

Seismic event deposits (seismites) have recently become a hot subject in sedimentology. Many kinds of seismites have been recognized in various sedimentary successions of different ages, in almost all sedimentary environments and from many geological settings around the world. However, detailed studies of specific seismites and their relationship to seismic activity of regional scale are still relatively underreported. Thus, this project would be the first attempt to relate the seismic activity that produced the seismite to regional tectonic event of North China Craton. We have selected three main rifts in North China Craton as the main area for our ongoing study of seismites because: (1) most of the successions in this area, which range from the Middle Proterozoic to Neo-Proterozoic, have been well-studied and their boundaries are clear; (2) the first seismite discovery in China was in the study area and (3) many new occurrences and varieties of extraordinarily well-preserved seismites have recently been discovered here. Since 2011, a number of well-preserved carbonate liquefaction mounds, liquefaction dykes and a carbonate sand volcano have been confirmed in the Mesoproterozoic Wumishan Formation in the Western Hills of Beijing. We also recently discovered many new, well-shaped carbonate sand volcanoes and other soft-sediment deformation structures in the same formation elsewhere in the Western Hills. The aim of this project is to discover new types of seismites and new seismically deformed layers in the Mesoproterozoic to Neoproterozoic successions elsewhere in the North China Craton in order to understand the relationship between ancient seismicity and major geodynamic events. To complete these goals, we will undertake a comprehensive investigation combining sedimentology, structural geology and ancient seismology. We plan to publish 4 to 6 papers and one guidebook regarding the seismic structures in the Meso-Neoproterozoic of the North China Craton over the next few years.

古地震记录亦称为地震事件沉积或震积岩，对于区域地层对比、恢复古地理环境和揭示长周期地震活动规律具有重要意义，已成为沉积学的热点。华北克拉通自中元古代始至新元古代经历了漫长的多期裂谷发育阶段，相继形成数个裂陷槽或裂谷，沉积了近万米厚的地层，蕴含了很多与克拉通伸展-裂解有关的古地震记录。对古地震记录的成因和时空分布规律等进行深入研究，将有助于反演克拉通的伸展-裂解过程。申请人已在中元古界雾迷山组发现了迄今世界上最古老的地震成因溢出丘、液化脉、沙火山、地裂缝和层间断层等，近期又在太行山北段雾迷山组中发现大量保存完好的沙火山和地裂缝等。基于上述发现和初步成果，本项目拟采用以沉积学为主的综合方法，对华北板块中-新元古界中的古地震记录进行系统研究，以查明其时空分布规律，从地震事件沉积方面为重塑华北板块构造环境演化提供依据。预计发表论文4-6篇，出版古地震记录图集一部，为地学研究和科学普及做出贡献。

地层中的古地震记录对于区域地层对比、恢复古地理环境和揭示一个地区长周期地震活动规律具有重要意义.华北克拉通自中元古代始至新元古代普遍沉积了数千米甚至上万米厚的地层，其中蕴含了很多与克拉通伸展-裂解有关的古地震记录。本项目采用沉积学为主的综合方法，对华北中新元古代和下古生代地层中的软沉积物变形现象做了广泛的野外调查，在几乎所有时代的地层中均发现了软沉积物变形。通过雾迷山组中硅质岩与白云岩中地震成因软沉积物变形构造的野外调查，已经发现了碳酸盐岩地层为主的海相地层中地震发生时产生的连续完美的变形序列，这个序列的岩性从完全固结的白云岩至半固结的白云岩，全程受地震作用以及硅质岩和白云岩的成岩过程控制，底部脆性岩中以白云岩的断裂和硅质岩的充填为主，向上过渡为硅质岩液化侵入到半固结的白云岩中，此现象比1969年Seismite(震积岩)的提出者赛拉赫(Seilacher)在美国蒙特利页岩(Monterey Shale) 剖面中发现的fault-graded beds现象更加典型。基于对高于庄组白云岩地层中的泥火山群的研究提出了“黏性沉积物中古地震触变流动变形构造模式”。野外调查过程中，在山西大同侏罗系中发现了国内尚未报道过的大量由地震触发的液化砂岩柱，它们是燕山运动在地层中留下的最直接证据，这一发现对于地层中经常出现的不明原因的结核也给出了一个合理的解释。在陕西宜川三叠系砂岩—页岩组合中也发现了地震液化砂岩柱和完整的砂火山，从而建立起了陆相盆地中地震触发的软沉积物变形模式。在泥河湾盆地第四系中发现大量软沉积物变形，通过对软沉积物变形的触发因素所做的系统总结和分析，特别是对国内外地震成因和冻融成因的软沉积物变形特征进行分析，我们发现这些变形主要为地震成因和冻融成因，并且以地震成因为主，这一成果对于认识泥河湾盆地的地质演化史以及分析泥河湾盆地的地层结构、环境考古提供了新的思路。