Mineral Magnetic Properties and Late Quaternary Transgressions Recorded by the Borehole WJ in the Taihu Plain, China

Abstract

With paleomagnetism and AMS14 C dating results, we reconstructed the depositional environmental evolution and marine transgression events during the Late Quaternary by examining the lithology, grain size, magnetic properties, and foraminifera of sediments from a borehole WJ in the Taihu plain of southern Yangtze Delta, China. We also investigated the application of magnetic proxies to distinguishing depositional environments in the estuarine-deltaic area. The results show that the sediment sequence of borehole WJ could be divided into four periods including Mid-Pleistocene stage I, Mid-Pleistocene stage II, Late Pleistocene, and Holocene. Their depositional geomorphological conditions were fluvial-lacustrine plain, coast-terrace, mouth bar-estuarytidal flat-terrace, and lacustrine plain, respectively. Three transgression events were revealed by the borehole WJ, which happened during the late stage of Mid-Pleistocene, marine isotope stage (MIS) 5 and MIS3 of LatePleistocene. The MIS5e transgression was the strongest one and the transgression in the late stage of MIS3 intensified significantly. Magnetic properties were strongest in the tidal flat and mouth bar sediments, with notably high values of χ lf , SIRM and HIRM.