Large earthquake-triggered liquefaction mounds and a carbonate sand volcano in the Mesoproterozoic Wumishan Formation, Beijing, North China

Abstract

Ten well-preserved, earthquake-triggered liquefaction mounds and a carbonate sand volcano have been found in the Mesoproterozoic Wumishan Formation (1550–1400Ma) in the Beijing area, North China. These features crop out in a roadcut near Zhuanghuwa Village. All ten mounds occur in the same sedimentary layer and have rounded shapes with some concentric and radial fissures arising from the centre. They range from 1.5 to 4m in diameter and from 10cm to 30cm in height. The carbonate sand volcano has a diameter of 110cm and the ‘crater’ at the top has a depth of about 30cm. Associated with these mounds and the sand volcano are many ‘normal’ sedimentary structures and numerous soft-sediment deformation structures. The former include ripple marks, cross-bedding, stromatolites and desiccation cracks, indicating deposition in a stable shallow-water peritidal platform environment. The latter include intrastratal faults and folds, seismically formed breccias and carbonate clastic dykes. The morphological features and the genesis of these liquefaction mounds are very similar to mounds formed recently by the great Wenchuan Earthquake of China (2008). Detailed thin-section study of the mounds found no signs of any kind of biological constructional process; instead it reveals some obvious fluidification and liquefaction characteristics. Comparative studies have shown that these features are probably the products of Mesoproterozoic earthquake activity. Copyright © 2013 John Wiley & Sons, Ltd.