南海东北部晚更新世以来沉积环境演变的矿物-地球化学记录

对南海东北部69柱(20°07.10'N,118°49.0'E)沉积物岩心进行碎屑矿物-地球化学特征研究,结果表明,以孔深165cm为界可划分出晚更新世末次冰期沉积和全新世冰后期沉积,这一地层划分结果与根据浮游有孔虫氧、碳同位素分析得出的结果是一致的.末次冰期时自生黄铁矿和硫元素高度富集,钠与铝、镁与铝和钠与钾的比值均较高,重矿物和SiO₂含量较高,CaCO₃含量较低,反映当时是一种相对闭塞的缺氧环境,气候干寒,化学风化作用较弱,以机械风化作用为主;研究区主要接受粒径较粗的硅质沉积;陆源物质的稀释作用可能是造成碳酸盐含量相对较低的主要原因.冰后期褐铁矿出现高含量,钠与铝、镁与铝和钠与钾的比值均降低,Al₂O₃和CaCO₃含量增高,反映沉积环境渐变为开放的氧化环境,气候转变为化学风化作用较强的湿热气候;研究区以接受较细粒的铝硅酸盐沉积为主,冰消期时还出现了碳酸盐保存高峰事件.

On mineralogical and geochemical records of paleosedimentary environmental variation in the northeastern South China Sea since the late Pleistocene

Based on the clastic mineralogical and geochemical characteristics, it is indicated that the core 69 with a length of 560 cm (20°07.10"N, 118°49.0'E; 2 971 m water depth) sampled by gravity piston corer from the north-eastern South China Sea could be divided into the late Pleistocene last glacial period and the Holocene epoch with a boundary at about 165 cm.This result consists with that of the oxygen and carbon stable isotopic analyses of planktonic foraminifers.During the last glacial period, there was a relatively closed anoxic environment, dry and cold climate, weak chemical weathering conditions which were suggested by the characteristics of higher content of heavy mineral with abundant authigenic pyrite, higher SiO₂ and S contents, and lower CaCO₃ content, as well as higher ratios of Na to Al, Mg to Al and Na to K in sedimentary samples.The sediments are composed mainly of siliceous deposits.The lower CaCO₃ contents of sediments might caused by the dilution of terrigenous components.In turn, during the postglacial period, the CaCO₃ and Al₂O₃ contents became higher, and the ratios of Na to Al, Mg to Al and Na to K decreased, which reflected that the sedimentary environment became an open oxidation environment, the climate became humid and hot with a stronger condition of chemical weathering.The sediments are composed mainly of aluminosilicate deposits.Furthermore, the maximum carbonate content occurs in the deglaciation period.