云南曲靖盆地晚始新世岩石磁学特征及意义  

Late Eocene rock magnetic characteristics of the Qujing basin,Yunnan and its significance

作　　者：杨永鹏 昝金波[1,3] 颜茂都 张伟林[1,3] 栗兵帅[1,2] 陈毅 张大文[1,2] 

机构地区：[1]中国科学院青藏高原研究所(大陆碰撞与高原隆升重点实验室),北京100101 [2]中国科学院大学,北京100101 [3]中国科学院青藏高原地球科学卓越创新中心,北京100101

出　　处：《地球物理学进展》2018年第1期133-141,共9页Progress in Geophysics

基　　金：国家重点基础研究发展规划(973)项目(2013CB956400);中国科学院战略性先导科技专项项目(B类)(XDB03020000);国家自然科学基金项目(41272185;41620104002;41571198;41172032;41672358);国家自然科学基金委重点国际(地区)合作研究项目(41620104002)联合资助

摘　　要：云南早新生代地层不仅记录了印度—欧亚板块碰撞以来早期的构造变形过程,还记录了大量区域气候和生物演化的信息,具有重要的科学研究价值.我们选取云南曲靖盆地晚始新世蔡家冲小屯组和蔡家冲组地层,尝试以环境磁学手段探讨晚始新世古环境的变化.主要通过地层的岩石磁学分析,结合沉积相变化,揭示出小屯组—蔡家冲组期间盆地经历了四个演化阶段,其中前三个阶段沉积相由河流—浅湖相逐渐演化为半深湖相,磁化率呈逐步降低的趋势;第四阶段伴随着火山碎屑物质的出现,磁化率值突然升高.根据典型样品的岩石磁学分析以及其他证据,揭示出磁化率值的降低主要受成壤作用减弱所导致的磁性矿物种类和含量的变化所引起.与通常气候变干冷造成的成壤作用减弱不同,该地层磁化率值的降低是由于沉积环境由河流—浅湖逐渐转变为半深湖,造成氧化环境逐步转变为还原环境,进而引起成壤作用减弱所造成.对于沉积环境变化的原因,可能由局部的构造运动造成或是气候变湿的影响.指示在相同物源环境下,磁化率值的变化在一定程度上响应古气候环境变化.因此,磁化率可作为早新生代气候环境变化研究的一种有效古气候代用指标.The early Cenozoic sedimentary sequences in Yunnan not only recorded the early tectonic deformation process of the IndiaEurasia collision,but also recorded regional climate and biological evolution,and have significant scientific research value. We carry out rock magnetic study of the Late Eocene Caijiachong-Xiaotun formations in the Qujing basin, Yunnan. Through magnetic susceptibility and sedimentary facies analyses,we establish four evolution stages in the Caijiachong-Xiaotun formations. The sedimentary environments evolved from river-shallow lake sedimentary facies to half deep lake sedimentary facies,accompanied by gradually reduced magnetic susceptibility values in the first three stages. Abrupt magnetic susceptibility values increase in the fourth stage, with the presence of pyroclastic material.Combined with other evidences, rock magnetic analyses of representative samples indicate that the reduce of magnetic susceptibility values was likely caused by pedogenesis weakening process that leading to the change of magnetic mineral type and content. Rather than a pedogenesis weakening process by dry and cold climate,the low magnetic susceptibility values were likely caused by a gradually transformation process from oxidation environment to a reduction environment, which was a result of changing sedimentary environment from river-shallow lake sedimentary facies to half deep lake sedimentary facies. Climate change and/or local tectonic activities might be the causes of the sedimentary environment change. Our study suggest that, the change of susceptibility value in certain degree responds to paleoclimate change in a unit source environment, and hence susceptibility can be used as an effective proxy in Early Cenozoic paleoclimate study.

关 键 词：云南曲靖 晚始新世 岩石磁学 成壤作用 

分 类 号：P318[天文地球—固体地球物理学]