南海北部中新世以来粘土矿物特征及东亚古季风记录

应用X射线衍射(XRD)、扫描电子显微镜(SEM) 和X射线能谱(EDS) 分析技术对南海北部ODP1146站中新世以来(~20 Ma) 粘土矿物的组成、结晶学特征、微形貌和化学成分进行了研究, 分析了粘土矿物的物质来源及其记录的东亚季风演化历史.1146站粘土矿物组合的总体特点是以伊利石和蒙脱石为主, 高岭石和绿泥石含量较低.物源分析表明, 1146站蒙脱石主要来自于吕宋岛, 伊利石和绿泥石来自于珠江和台湾(长江), 而高岭石则主要来自于珠江.1146站的粘土矿物不仅被南海周围物源的同时代气候所控制, 而且为相互消长的不同传输作用(表层洋流) 的强度所影响.1146站(伊利石+绿泥石) /蒙脱石比值可以用来作为东亚季风演化的矿物学标志.指标变化显示出东亚冬季风强度和冬季风相对夏季风的强度在15 Ma、8 Ma和3 Ma左右发生了3次显著加强, 结果可以与黄土、北太平洋风尘沉积、南海微体古生物记录等很好对比.青藏高原的阶段性隆升可能促进了东亚季风的这3次加强. 

Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene

Clay mineral assemblages,crystallinity,chemistry and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea(SCS)were analyzed and used to trace sediment sources and obtain proxy records of past changes in the East Asian monsoon climate since the Miocene based on a multi-approach including X-ray diffraction(XRD)and scanning electron microscope combined with energy dispersive X-ray spectrometer(SEM-EDS).Clay minerals mainly consist of illite and smectite,with associated chlorite and kaolinite.The illite at ODP Site 1146 has very well-to-well crystallinity,and smectite has moderate-to-poor crystallinity.In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like,a typical micromorphology of volcanic smecites.The smectite at ODP Site 1146 is relatively rich in Si element,but poor in Fe,very similar to the smectite from the West Philippine Sea.In contrast,the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess,Yellow River,Yangtze River,and Pearl River.Sediment source studies indicate that smectite originates mainly from Luzon,kaolinite from the Pearl River and illite and chlorite from the Pearl River,Taiwan and/or the Yangtze River respectively.The clay mineral assemblages at ODP Site 1146 were not only controlled by the continental weathering regimes surrounding the SCS but also by the changing strength of the transport processes.The ratios of(illite chlorite)/smectite at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution.The consistent variation of this clay proxy with those from loess,eolian deposition in the North Pacific and planktonic and benthic foraminifera,and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity,aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon,occurred at ~15 Ma,~8 Ma and the youngest at about 3 Ma.The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma,8 Ma and 3 Ma.