伶仃洋东岸晚更新世以来硅藻组合及环境意义

Diatom assemblage since late Pleistocene in the east coast of Lingdingyang Bay and its environmental implications

通过分析伶仃洋东岸sz17QZ-20-3钻孔硅藻分布特征,结合测年、岩性和粒度,重建了该地区晚更新世以来的古环境演化。依据沉积物岩性粒度变化判断,晚更新世时期在23.6~11.0 m层段发育了一套河床相-溺古湾相-岸滩相-冲积相的垂向沉积序列,在花斑黏土层中有海水种Ethmodiscus rex碎片的存在,指示晚更新世海侵海退旋回。早全新世海侵在9000 cal.aBP左右到达研究区,海水种硅藻含量开始迅速增加,发育滨海平原相沉积;在8000 cal.aBP左右达到最高海平面,海水种硅藻含量最高;随后研究区处于海平面停滞状态,并缓慢下降,发育浅海相沉积;中晚全新世4.2~0 m层段为海退时期,发育河口湾相沉积。中全新世4.4~4.2 m层位海水种含量突然增加和4.4~4.6 m层位贝壳碎屑层指示可能有风暴潮事件发生;晚全新世0.3~0 m层段表层沉积物中硅藻丰度异常偏高,受人类活动影响较大。

Based on the distribution pattern of diatom in the borehole of sz17QZ-20-3 of Lingdingyang Bay,with the support of dating,lithology and grain size distribution data,the paleoenvironment evolutionary history since late Pleistocene of this area is reconstructed.According to the change in lithology and grain size of the sediments,a vertical sequence consisting of river bed facies-drowning valley bay facies-beach facies-alluvial facies upwards was established for the interval of 23.6~11.0 m of Late Pleistocene.The presence of Ethmodiscus Rex fragments of marine species in the variegated clay layer indicates the cyclic transgressive and regressive sequences of the late Pleistocene.Early Holocene transgression reached the research area around 9000 cal.aBP,the diatom content of marine species rapidly increased,and the coastal plain facies was rather developed.The highest sea level was reached around 8000 cal.aBP,with the highest content of diatom of marine species.The sea level was falling after a period of stability and shallow marine deposits dominate;The Middle-Late Holocene or the interval of 4.2~0 m indicates a regressive period dominated by estuarine facies.The sharp increase in marine species at 4.4~4.2 m horizon in addition to shell debris at 4.4~4.6 m horizon of Middle Holocene indicates storm surge events;the diatom abundance in surface sediments at 0.3~0 m horizon of Late Holocene is unusually high under the influence of human activities.