晚新生代以来青藏高原中部环境演化过程的地球化学证据  

Geochemical Records of Environmental Evolution in the Last 2. 8 Ma from the Co Ngoin, Central Tibetan 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湖泊沉积与环境重点实验室

出　　处：《地质学报》2004年第2期234-241,共8页Acta Geologica Sinica

基　　金：国家重点基础研究发展规划项目(编号G1998040810)

摘　　要：青藏高原中部发育一系列独立的内流断陷湖盆,其中位于南亚季风区边缘的错鄂湖盆发育了巨厚的湖泊沉积,是研究高原内部地质环境变迁与构造-气候旋回的理想场所。本文对青藏高原中部错鄂孔197m沉积岩心Sr、Rb、Zr含量及其比值以及沉积物有机质δ^(13)、TOC含量进行了分析,同时结合岩性、粒度、粘土矿物组成,初步建立了青藏高原中部2.8Ma来岩石化学风化的相对强度和古环境演化过程。研究表明,2.8Ma来青藏高原中部经历了三次剧烈的环境演化过程:在约197～170m(2.8～2.5Ma)之间,低Sr含量,高Rb/Sr和Zr/Rb值记录了较弱的化学风化过程,δ^(13)C、TOC含量反映气候前期暖干,后期偏凉湿,揭示冷湿气候的云杉林突然增加,沉积岩性明显变粗,反映了一次强烈的构造隆升运动;在约170～38.5m(约2.5～0.8Ma)之间,高Sr含量,低Rb/Sr和Zr/Rb值记录流域经历较强的化学风化过程,δ^(13)C、TOC含量反映高原中部总体处于温湿或凉湿的环境下,沉积岩性较细,高原总体处于相对剥蚀夷平阶段;在38.5～0m(约0.8～0Ma)段,Sr含量处于相对低值,Rb/Sr值相对较高,化学风化相对较弱,δ^(13)C、TOC含量表明高原中部处于较寒冷的环境之中,沉积岩性的再次明显变粗表明高原中部又经历了一次强烈的构造运动,并使高原中部整体隆升到4000m以上,奠定了现?A series of independent faulted inland lake basins are developed in the central Tibetan Plateau, among which the Co Ngoin Basin is located at the margin of the Indian monsoon with thick lacustrine sediment. The sediment is a perfect record for studies on the paleoenvironmental changes and tectonic-climatic cycles. In this paper, the authors present a high-resolution vertical distribution of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ13C, TOC in the sediment from the Co Ngoin, Central Tibetan Plateau, and by a combination with the lithological properties, grain size distribution and clay mineralogy, discuss the chemical weathering process and reconstruct the history of the weathering intensity and paleoclimatic change in the last 2. 8 Ma. The sedimentary proxy records indicate that there are three strong environmental evolution processes. In the core depth of 197~170m (about 2. 8~2. 5 Ma) , the relatively low Sr content, and high Rb/Sr and Zr/ Rb ratios show a low intensity of chemical weathering in the Co Ngoin watershed, and the values of δ13C and TOC indicate a warm-dry to cool-wet climate. The sudden occurrence of subalpine coniferous forest shown from the core from the Co Ngoin and apparent changes in lithology with coarse sand and gravel sediments reflected a strong rising. The higher Sr content, lower Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering period between 2. 5 Ma and 0. 8 Ma (in the core depth of 170~38. 5 m), and the δ13C and TOC reveal a warm/cool and wet plateau climate. The lithology was characterized by mud and silt to fine sandy mud, probably indicating a process of denudation and relatively tectonic stable epoch of the Plateau. In the depth of 38. 5~0 m (about 0. 8~0 Ma?) , the relatively low Sr content, high Rb/Sr and Zr/Rb ratios record a relatively low intensity of chemical weathering, and the values of δ13C and TOC reflect a cold climatic period. The coarse sand and gravel sediments indicate a strong tectonic movement again. The plateau uplifted t

关 键 词：青藏高原 环境演化 新生代 地球化学 

分 类 号：P534[天文地球—古生物学与地层学]