青藏高原晚始新世干旱化事件:改则盆地康托组碳酸盐岩碳氧同位素的记录

The Late Eocene Aridification of Tibetan Plateau:Evidence from Carbon and Oxygen Isotopes of Kangtuo Foramtion Primary Carbonates in Gaize Basin

改则盆地位于青藏高原腹地,盆地内沉积物记录了高原古环境变化的重要信息。本文对改则盆地康托组碳酸盐岩碳氧同位素进行研究,结果显示改则盆地中-晚始新世的演化分为两个阶段:1中始新世湿润气候下开放湖盆阶段:虽然碳酸盐岩δ^(18)O值在43层处向正值偏移,但整体^(18)O和^(13)C强烈亏损,并且该时期碳酸盐岩δ^(18)O值和δ^(13)C变化相关系数为R^2=0.082。表明该阶段的研究区虽然经历过短期蒸发作用增强或补给水减少,但整体是气候湿润条件下补给水丰富的开放型湖盆。2晚始新世干旱气候下封闭湖盆阶段:经过中新世晚期(63层)气候和湖泊水文状态的过渡,晚始新世^(18)O和^(13)C同位素富集,δ^(18)O值和δ^(13)C值变化相关系数为R^2=0.7762。表明该阶段气候干旱,蒸发作用强烈,湖盆萎缩成为封闭湖盆。综合前人研究,认为青藏高原腹地及北缘、东北缘在晚始新世存在明显的区域性干旱化事件。对比分析青藏高原隆升、全球气候记录、全球海水Sr和大气CO_2记录,认为青藏高原腹地和北部的干旱化事件主要受青藏高原隆升的影响。

Gaize Basin located at in hinderland of Tibetan Plateau, whose sediments recorded significant palaeoclimatic information of Tibetan Plateau. Carbon and oxygen isotopes of Kangtuo Formation in Gaize Basin were test in this study. The results indicate that Gaize Basin experience two evolution phases during Middle-Late Eocene： ① the Middle Eocene open lake under humid climatic setting： In this period, carbon and oxygen isotope are strong depleted and just positive shift in oxygen isotope values at 43 layer. And the correlation between carbon and oxygen isotope variations is low （R^2 =0. 082）. These records indicate that Gaize basin is an open lake with abundance inflow water in humid climate during this phase, although it has experience a short term strong evaporation or decrease of inflow water. ② the Late Eocene closed basin in dry climate： In this phase, oxygen and carbon isotope become enrichment, consistently. And, the correlation coefficient between carbon and oxygen isotopic variations is high （R^2 =0. 7762）. Inferred from these records, Gaize basin experienced strong evaporation in arid climate, and, shrunken into a closed basin, gradually. The Late Eocene aridification is a regional event in the hinderland and northern of Tibetan Plateau, based on the previous paleoclimatic studies. Analysis of the uplift of Tibetan Plateau, Global paleoclimatic records, seawater strontium isotope curve and global Pco2 curve, the Late Eocene aridification could be mainly affected by the uplift of Tibetan Plateau.