Sedimentary records of paleoseismic events in the Late Pleistocene sediments of the Southern Yangtze River deltaic plain, East China, and their implications for differential subsidence of the Taihu block

摘要

Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary fades assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude 5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.