珠江三角洲中山地区ZK201-2钻孔硅藻组合及古环境意义

DIATOM ASSEMBLAGES FROM BOREHOLE ZK201-2 IN ZHONGSHAN AREA OF THE ZHUJIANG RIVER DELTA GUANGDONG,S.CHINA AND THEIR PALEOENVIRONMENT SIGNIFICANCE

经对珠江三角洲中部中山地区ZK201-2钻孔86个岩芯样品进行硅藻分析,鉴定出45属168种(包括未定种和变种),分属海水种、半咸水种和淡水种3种生态类型,据其组合状况和部分典型属种的现代生态环境指示意义,结合钻孔地层沉积特征和AMS14 C测年结果,在该孔自下而上确定了6个组合带。组合1 Ethmodiscus rex-Cyclotella striata-Paralia sulcata和组合2 Cyclotella striata-Paralia sulcata-Coscinodiscus divisus中硅藻均发生明显溶蚀现象,样品中个体数量(丰度)变化较大,两组合分别对应晚更新世河口湾相及末次盛冰期花斑粘土风化沉积层;组合3 Gomphonema kaznakowii-Cymbella affinis-Eunotia clevei,组合4 Paralia sulcata-Coscinodiscus divisus-Coscinodiscus excentricus,组合5 Cyclotella striata-Paralia sulcata-Nitzschia cocconeiformis和组合6 Cyclotella striata-Coscinodiscus blandus-Coscinodiscus divisus,分别对应全新世河漫滩-滨海河湾、潮滩相、河口湾相、河口坝-湿地沉积。该钻孔硅藻分析结果表明研究区晚更新世晚期以来经历了海洋氧同位素MIS3和MIS1期两次较大的海侵海退旋回。

Based on the diatom analyses of 86 core samples collected from the borehole ZK201-2 which is located at the Zhongshan area of the Zhujiang River Delta, a total of 168 species （including sp. indet, and var. ） in 45 genera of dia- toms belonged to 3 types of ecological groups, i. e. , marine-, brackish- and freshwater were identified. According to the diatom assemblage situation and ecological environment signification of some typical species, as well as the litho- logical characteristics of strata and calibrated AMS14C age at the studied borehole, six diatom assemblages referred to different sedimentary facies Were recognized from bottom to top. Diatom assemblage 1 （Ethmodiscus rex-Cyclotella striata- Paralia sulcata ） and assemblage 2 （Cyclotella striata-Paralia sulcata-Coscinodiscus divisus ） characterized by poor preservation with severe dissolution, indicate the paleoenvironment changes from the Late Pleistocene estuary conditions to the weathered sedimentary layer during the Last Glacial Maximum. The diatom assemblage 3 （Gompho- nema kaznakowii-Cymbella a f finis-Eunotia clevei ） , assemblage 4 （ Paralia sulcata-Coscinodiscus divisus-Coscino- discus excentricus）, assemblage 5 （Cyclotella striata-Paralia sulcata-Nitzschia cocconeiformis） and assemblage 6 （Cyclotella striata-Coscinodiscus blandus-Coscinodiscus divisus）, corresponded to the alluvial flat or sluggish river, estuary, estuary dam or wetland facies of delta ＇front respectively. Above-mentioned change of diatom assemblages suggests that two transgressive-regressive cycles, corresponding to MIS3 and MIS1 respectively since late Late Pleis- tocene, can be recognized in the study area.