摘要
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 lay er, 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 soft sediment deformation structures, the occurrence frequency of palaeoearthquake of the Wumishan deposi tional period is calculated as between 32 thousand years to 20 thousand years.关键词
中元古界雾迷山组/永定河/软沉积物变形/古地震Key words
Mesoproterozoic Wumishan Formation/ Yongding River/ soft-sediment deformation/ palaeoearthquake分类
天文与地球科学
