冲绳海槽南部柱状沉积物地球化学特征及其古环境意义

GEOCHEMICAL CHARACTERISTICS FOR CORE SEDIMENTS OF THE SOUTHERN OKINAWA TROUGH AND THEIR PALEOENVIRONMENT IMPLICATION

对冲绳海槽南部 E0 17柱状沉积物进行了地球化学分析 ,结果表明 ,该柱状沉积物主要的化学组成为Si O2 、Al2 O3、Ca O和 TFe2 O3(全铁 ) ,K2 O、Na2 O、Mg O和 Mn O次之 ,具有明显的东海陆架沉积特征 ,但微量元素明显富集。 R型因子分析可将该柱状沉积物的化学组成划分为 5种组合类型 :(1) Si O2 、Na2 O、Zr、Al2 O3、K2 O、TFe2 O3、Mg O、Co和 Cr;(2 ) Ca O和 Sr;(3) Si O2 、Na2 O和 Zr;(4) Cu、Pb、Zn和 Ni;(5 ) Mn O和 Ba。根据元素在垂向上的协同变化关系 ,前 3个元素组合分别对应于陆源碎屑沉积、生源沉积和火山沉积 ,后两个元素组合主要与早期成岩过程中元素的再分配和自生沉积作用有关。氧同位素和 AMS1 4C的测年结果表明 ,该柱状沉积物属于末次冰消期 (约 15 ka BP)以来的沉积 ,全新世和末次冰消期的界线在 175 cm左右。与全新世相比 ,末次冰消期沉积速率较高 ,沉积物的粒度相对较粗 ,陆源碎屑组分 Si O2 、Al2 O3、K2 O等相对较高 ,生源组分 Ca O和

Geochemical characteristics of core E017 sediments were analysed. The core was sampled in the south Okinawa Trough. The main chemical compositions of the core sediments are SiO 2,Al 2O 3,CaO and TFe 2O 3,and then K 2O,Na 2O,MgO and MnO, which are similar to those of the shelf sediments in the East China Sea,but trace elements are richer in the core sediments. Based on the result of R model factor analysis,the chemical compositions of the core sediments can be classified into five groups:①SiO 2,Na 2O,Zr,Al 2O 3,K 2O,TFe 2O 3,MgO,Co and Cr;②CaO and Sr;③SiO 2,Na 2O and Zr;④Cu,Pb,Zn and Ni; and ⑤ MnO and Ba.Based on the identical variation of the elements, the former three element groups are correspondent to terrigenous debris deposit, biogenic deposit, and volcanic deposit respectively,and the latter two element groups are related to the redistribution of the elements and autogenic deposit of the early diagenesis. Based on the results of O isotopic analysis and the AMS 14 C dating, the core sediments belong to deposit from the last deglaciation (about 15 kaBP) to present,the boundary between the Holocene epoch and the last deglaciation is located at about 175 cm. In this stratigraphic scale, the grain size and chemical compositions of the core sediments vary with the paleoenvironmental conditions. Compared with the Holocene epoch, the sedimentation velocity of the last deglaciation is higher, the grain size is coaser and the terrigenous debris elements such as SiO 2,Al 2O 3,K 2O are richer, and the biogenic elements such as CaO and Sr are relatively low.