【摘要】 北京地区中元古界雾迷山组是太古界至中生界中出露面积最广、沉积厚度最大的地层单元,岩性以白云岩为主,其次为硅化白云岩。雾迷山组层序稳定,形成于相对广阔、持续且稳定沉降的浅水沉积环境。在永定河流域自庄户洼村溯河而上直至珍珠湖景区,在不同层位的雾迷山组露头中集中发现了多个期次、不同规模、由古地震引发的软沉积物变形构造,包括液化变形(液化混插、底辟、液化脉及液化卷曲层理等)、挤压变形(紧密褶皱、板刺状角砾和丘—槽构造等)、拉伸变形(环状层、拉伸布丁)以及脆性变形(地裂缝、层间断层和震裂岩)。文中对这些软沉积物变形的分布和表面特征做了系统描述,对典型的液化变形、挤压变形及拉伸变形的形成机制从形态学上进行了计算机模拟。结合该区的构造背景和前人研究资料,认为该区雾迷山组沉积期古地震系沿中元古代燕辽裂陷槽轴部的断裂活动触发的;根据软沉积物变形的出现频率,对古地震发生频率(地震周期)进行了初步估算,约为3.2至2万年。更多还原

【Abstract】 As the most widely distributed and the thickest deposited stratigraphic unit in Beijing area,the Mesoproterozoic Wumishan Formation was mainly composed of dolostone and siliceous dolostone and was basically formed in a relatively long stable peritidal environment.The sedimentary records formed in such environment are allergically to the changes of palaeoearthquakes and are rather easily preserved. Numerous soft-sediment deformation structures of palaeoearthquake origin have been identified in the upper part of Wumishan Formation along the Yongding River Valley(from Zhuanghuwa to Zhenzhu Lake).Typical soft-sediment structures described in this paper include liquefied structures(liquefied mixed layer,diapir,liquefied vein,liquefied convolute bedding),compressional deformation structures(intense fold,plate-spine breccia structures,mound-and-sag structure),extensional structures(loop-bedding, extensional pudding) and brittle deformation structures(ground fissure,intrastratal fault,seismic cracked breccia).Formation processes of typical soft-sediment deformation structures are morphologically simulated by computer.Combined the regional geological background and former geologists’ research achievements,the movement of main fault along the axial region of Yan-Liao aulacogen is identified as the triggering fault of palaeoearthquake since the Early Mesoproterozoic.According to the frequencies of softsediment deformation structures,the occurrence frequency of palaeoearthquake of the Wumishan depositional period is calculated as between 32 thousand years to 20 thousand years.更多还原