南海北部陆架中全新世沉积记录及古环境意义

 通过分析珠江口外陆架C069孔沉积柱样的粒度、黏土矿物、主量元素及底栖有孔虫，来研究南海北部中全新世晚期古环境演化。4.2 ka前为全新世大暖期后期，气候湿润，珠江口外陆架受大量的珠江淡水影响，导致C069孔位置的水动力条件较强，形成下段粒度较粗的碎屑沉积物，高岭石含量较高，低的MgO/Al2O3比值，以及受冲淡水影响形成的底栖有孔虫。由于受4.2 ka的极冷事件的影响，C069孔上段的沉积环境受珠江冲淡水影响减小，水动力条件减弱，沉积物粒度变细，高岭石含量降低，MgO/Al2O3比值增大，形成正常浅水环境的底栖有孔虫。4.2 ka以后，台湾来源物质的贡献增多，导致沉积物中伊利石和绿泥石的含量增多，伊利石结晶度和化学指数值都明显变小。

Records and Plaeoenvironmental Implications from the Shelf of the Northern South China Sea since the Mid-Holocene

High resolution records as lakes,peats,speleothems are reported to study the hydrological exhibition of 4.2 ka BP event in China in recent years.The terrigenous clastic matter in continental shelf could reveal sedimentary environment evolvement and paleoclimate.Sediment grain size,clay mineral,major elements,and benthic foraminifera of the Core C069(113 49’ E,21 15’ N,length: 2.1 m),which is from inner shelf of the northern South China Sea,have been investigated to reveal sedimentary environment evolvement and paleoclimate.The results indicate that sediments became finer and well from bottom to top.The frequency distribution curves of grain size in the lower segment(1.1~2.1 m) are poorly sorted with bimodal distribution,which display the strong hydrodynamic condition.However,in the upper segment(0~1.1 m) after 4.4 ka,the sediments have single peak frequency distribution curves.The coarse sediments derived from the Pearl River.The clay mineral assemblage consists dominantly of illite,lesser abundance of kaolinite and chlorite,with scare smectite.Kaolinite of the northern South China Sea is dominartly originated major origin from the Pearl River,predominant illite and chlorite from Taiwan,and principal smectite from the Luzon islands.The content of kaolinite decreases from 27%(1.1~2.1 m) to 18%(0~1.1 m),and illite crystallinity and illite chemistry index decrease similarily.The upper segment with more illite displays that more contribution of illite from Taiwan carried by surface currents,result in lower illite crystallinity and chemistry index.The results suggest that clay mineral assemblages in the inner shelf of the northern South China Sea are mainly controlled by provenance supply and downcore records do not bear contemporaneous paleoclimatic features.The benthic foraminifera dominant species in the lower segment are Ammonia becarii and Ammonia dominicana,which lived in brackish environment where the water was influenced by Pearl River diluted water.However,the benthic foraminifera dominant species changed with Cibicidoides subhaidingarii,Ammonia compressituta in the upper segment,which lived in normal shallow water environment.MgO/Al2O3 ratio increased from bottom to top due to the less terrigenous clastic matter transported to inner shelf of the northern South China Sea in extreme dry-cold after 4.2 ka.The lower segment sediments contain higher kaolinite content;lower MgO/Al2O3 ratio,with benthic foraminifera dominant species lived in brackish environment where the water was influenced by Pearl River diluted water in the Holocene Megathermal.However,the upper segment sediments contain lower kaolinite content,higher MgO/Al2O3 ratio in the upper segment,displaying that less Pearl River’s contribution in extreme dry-cold time since 4.2 ka.