Discovery of Mesoproterozoic seismites Baishi Mountain, Hebei Province and its geological significance

摘要

Seismically collapsed megabreccias (seismites) have been found in the lower part of the Second Member of the Mesoproterozoic Wumishan Formation (1.0~1.4 Ca), along the tour route of the Baishi Mountain tectonic "peak forest" in Laiyuan County, Hebei Province These megabreccias are controlled bytwo synsedimentary normal faults and formed instantaneously subaqueously from collapsed fault-cliff rocks. According to the scale of the seismites and the degrees of down- faulting of the two faulting, it is estimat-ed that the strength of the Baishi Mountain earthquake may have reached magnitude 8± of the Richter scale. The earthquake was a concrete manifestation of the stage of repeated occurrence of Mesoproterozoic seismic catastrophic event in North China. As Baishi Mouvtain is less than 10 km from the ancient Tai- hangshan deep fault and the Baishi Mountain seismites extends in a NNE direction as is the case with itssynchronous normal fault and Taihangshan deep fault, it is inferred that then at that time the Baishi Mountain area might have been within the influence of the activity of the Taihangshan fault zone.