太湖平原WJ孔矿物磁学特征以及晚第四纪海侵事件

Magnetic properties of minerals recorded by the borehole WJ and Late Quaternary transgressions in the Taihu plain,southern Yangtze Delta

基于古地磁和AMS14 C定年结果,对长江三角洲太湖平原的WJ孔进行岩性特征、矿物磁学、粒度分析及有孔虫化石研究,拟重建WJ孔记录的晚第四纪以来沉积环境演变过程与海侵事件,并探讨环境磁学参数对河口三角洲地区沉积环境演化的指示意义.研究结果表明,WJ孔可以划分为中更新世阶段I、中更新世阶段II、晚更新世、全新世四个阶段,沉积地貌环境分别为:河湖、滨海—阶地、河口坝—河口湾—潮滩与阶地、湖沼平原.WJ孔揭示了三次海侵事件,分别为中更新世晚期海侵,晚更新世MIS5海侵和晚更新世MIS3海侵.其中记录的MIS5e海侵最为强盛,MIS3后期也存在一次海侵加强事件.另外,滨海潮滩—河口坝环境的沉积物磁性特征明显,χlf、SIRM、HIRM等为显著高值.

Based on paleomagnetism and AMS14 C ages, we reconstructed the evolution of sedimentary environment and transgression events during the Late Quaternary by examining thelithology, magnetic properties, grain sizes, and foraminifera of sediments from a WJ in the Taihu plain, southern Yangtze Delta, China. We also examined the borehole named applications of magnetic proxies to distinguishing depositional environments in the estuary-delta area. The results show that the sediment sequence of the WJ borehole can be divided into four periods, i. e. Mid-Pleistocene stage I, Mid-Pleistocene stage II, Late-Pleistocene, and Holocene. Their depositional geomorphological conditions were fluvial-lacustrine, coastal-terrace, mouth bar- estuary-tidal flat-terrace, and lacustrine plain, respectively. Three transgression events were detected in the borehole WJ, which happened during the late Mid-Pleistocene, MISS and MIS3 of I.ate Pleistocene. Among them, the MISSe transgression was the strongest one. Additionally, the transgression was intensified significantly in late MIS3. Magnetic properties were strongest for the tidal flat and mouth bar sediments with notably high values of Xlf, SIRM and HIRM.