近4400年来南海北部陆架沉积地球化学记录及其地质意义

Geochemical Records and Geological Significance of the Continental Shelf Sediments in the Northern South China Sea Since 4400 a

对位于海南岛南部陆架的S20孔沉积物进行了沉积学、AMS14C年代、粒度和常微量元素分析,初步探讨了该区物质来源及蕴含的亚洲季风演化信息。近4400a以来,S20孔岩性较均一,其沉积作用受相对单一而稳定的水动力条件控制。S20孔沉积物源区物质硅酸盐矿物经历了明显的风化,A—CN—K图示和较低的CIA值(小于66)指示了源区较低的化学风化程度。海南岛东部河流和珠江物质是最为可能影响S20孔区域的两个来源,由于对海南岛河流物质的研究相当匮乏,本研究尚无法定量估算该两个可能物质来源的各自贡献。S20孔沉积物CIA、Al2O3/Na2O、CaO*/TiO2、Na2O/TiO2等变化主要反映的是源区物质风化程度变化,该孔沉积物源区化学风化程度自4400～1600aBP逐渐减弱以及1600aBP以来的逐渐增强,与中国南部Dongge洞石笋氧同位素曲线记录的亚洲夏季风变化趋势对应良好,说明该区沉积物中蕴含了丰富的亚洲季风变化信息。S20孔沉积物揭示出的化学风化程度强弱可能主要受控于轨道时间尺度上北半球夏季太阳辐射量变化。南海陆架区沉积物中物源与季风演化等信息的提取,亟待更多更高精度研究工作的展开。

Lithology,AMS14C dating,grain-size,major and trace element analysis were carried out for Core S20,which was retrieved from the continental shelf in the northern South China Sea（SCS） .Sediment provenance and evolution history of Asian monsoon were discussed in this paper.Since 4400 a BP,the lithology of Core S20 is homogenous,the hydrodynamic conditions in the study area is relatively stable.The silicate material in the source area experienced significant weathering processes.A-CN-K plot and low CIA（chemical index of alteration） value indicated a lower degree of chemical weathering.The river in the eastern Hainan Island and Pearl River is the two most likely sources of the study area.Because of inadequate research on the former,this study could not quantitatively estimate their possible contributions.The variations of CIA,Al2 O3 /Na2 O,CaO /TiO2 and Na2 O/TiO2 value mainly reflect the degree of weathering of the source area.Gradually weakened weathering between 4 400 ～ 1 600 a BP and strengthened from 1600 a BP to nowadays well corresponded to the absolute-dated oxygen isotope record from Dongge stalagmite,southern China,indicating that the core sediments in the study area containing a wealth of information on the evolution of Asian monsoon.The degree of chemical weathering of sediments in the northern SCS is mainly controlled by the variation of orbitally-induced Northern Hemisphere summer insolation.More research work with high resolution is necessary for extracting information on sediment provenance and monsoon evolution in the Northern SCS shelf.