长江三角洲南部地区晚更新世年代地层和海水进退

CHRONOSTRATIGRAPHY AND TRANSGRESSION/REGRESSION DURING LATE PLEISTOCENE IN THE SOUTHERN CHANGJIANG (YANGTZE) RIVER DELTA PLAIN

根据长江三角洲晚第四纪 4个钻孔详细的测年和微体古生物分析结果 ,对该区约 110kaBP来的地层进行了年代学划分 ,并且重建了晚更新世海侵海退过程。研究发现 ,形成于 12 0～ 110kaBP的蓝灰色硬土是本区晚更新世底界的标志 ,而晚更新世顶界的标志是形成于 17～ 10kaBP的暗绿色或棕黄色硬土。晚更新世早期 110～ 6 0kaBP间 ,本区主要发育河流相的含砾砂 ,但其中 10 0～ 80kaBP间发生一次较弱海侵 ,以溺谷相沉积为主。晚更新世中期 6 0～ 2 2kaBP ,沉积物经历粗 -细 -粗 3个阶段 ,分别是 6 0～ 4 0、4 0～ 34和 34～ 2 2kaBP。其中第 2阶段在西部地区出现硬土层 ,而中东部地区 6 0～ 2 2kaBP期间海侵层连续 ,且在 4 3～ 4 0和 34～ 2

Dating and microfossil analysis was conducted on four boreholes of late Quaternary deposit in the southern Changjiang(Yangtze)River delta plain to characterize the chronology and sea-level changes during the late Pleistocene. Our work shows that the blueish gray stiff mud at core depth of 100～145 m was deposited from ～110 to 120 kaBP, serving as the symbol of the end of the mid Pleistocene. The dark green or brownish yellow stiff mud at core depth of 15～30 m was deposited from 10 to 17 kaBP, serving as the end of the late Pleistocene. Fluvial gravelly sand prevailed in the study area during 110～60 kaBP, and a weak transgression occurred during 100～80 kaBP, forming a drowned valley. Three sedimentary sequences (coarse-fine-coarse) appeared from 60 to 40 kaBP, from 40 to 34 kaBP, and from 34 to 22 kaBP respectively. Stiff mud was found in the west part of the study area during 40～34 kaBP. Continuous transgressive deposits of 60～22 kaBP were found in borehole MFC. Two strongest sea-level changes were discovered at 43～40 kaBP and 34～22 kaBP respectively.