湖泊沉积物记录的藏中地区2.8Ma以来的环境演变历史  

Lake sedimentary records of environmental evolution in the last 2.8 Ma from the Co Ngoin Basin, central Qinghai Xizang Plateau

作　　者：陈诗越[1] 王苏民[1] 金章东[1] 沈吉[1] 

机构地区：[1]中国科学院南京地理与湖泊研究所

出　　处：《地球化学》2004年第2期159-164,共6页Geochimica

基　　金：国家重点基础研究发展规划项目(G1998040810)

摘　　要：对青藏高原中部错鄂钻孔岩芯湖泊沉积物δ13C、总有机碳(TOC)、总氮(TN)、C/N和Rb/Sr比值等进行了分析,并结合岩性、孢粉组合特征等,建立了2.8Ma以来藏中地区的环境演化序列、区域构造活动和湖盆演化过程。研究显示,大约在2.8Ma,错鄂构造成盆,2.6Ma的构造运动之后,湖泊扩张,夏季风降水增加,湖泊沉积物以青灰色泥为主,藏中地区总体上处于温湿或凉湿的环境下;约0.78Ma后,沉积岩性明显变粗,湖盆快速充填,反映了强烈的构造隆升运动,并使高原中部整体隆升到4000m以上,δ13C和TOC反映藏中地区环境具明显的高寒特点;高原剧烈隆升时期,化学风化较弱,而在高原相对稳定的剥蚀夷平阶段,化学风化较强,说明藏中地区的化学风化在受气候强烈影响的同时,又受高原阶段性的构造隆升所控制。A series of independent faulted inland lake basins are developed in the central Qinghai Xizang Plateau, among which the Co Ngoin Basin is located at the margin of Indian monsoon with a thick lacustrine sediment. The sediment of Co Ngoin is a perfect record for studying on paleoenvironmental change and tectonic climatic cycles. The paleoenvironmental changes, regional tectonic movement and the evolutionary process of the Co Ngoin Basin during the last 2.8 Ma are reconstructed based on the analysis of δ13C, TOC, TN, C/N, Rb/Sr ratio, and by combining with lithological property and pollen from the central Qinghai Xizang Plateau. The sedimentary records indicate that the basin was first formatted by fault activity at about 2.8 Ma, and after the strong tectonic movement at 2.6 Ma the lake enlarged and the rainfall of summer monsoon increased. The δ13C, TOC reveal a warm/cool and wet plateau climate and the sediment is characterized by the grayish mud. The coarse sand and gravel sediments indicate a strong tectonic movement after 0.78 Ma and the plateau uplifted to above 4 000 m. The values of δ13C and TOC reflect a cold climatic period. The Rb/Sr ratio records a strong intensity of chemical weathering at the weak denudation and relatively tectonic stabilize period of the plateau and a weak chemical weathering at the strong tectonic movement epoch in the Co Ngoin watershed. Studies show that the chemical weathering and the major environmental changes are affected by the climatic changes, and also largely controlled by stepwise uplift of the Qinghai Xizang Plateau.

关 键 词：湖泊沉积 地球化学 化学风化 环境演化 青藏高原 

分 类 号：P512.2[天文地球—地质学] X142[环境科学与工程—环境科学]