【作者】 李朝柱；

【导师】 蒋复初；

【作者基本信息】 中国地质科学院 ， 第四纪地质学， 2012， 博士

【摘要】 龙街粉砂层为—套灰黑、灰黄、灰白色的粉砂、粘土质粉砂和粘土为主的水平地层,主要沿金沙江三堆子至白马口段河谷两岸分布,其中以元谋地区的龙街盆地最为发育。龙街粉砂层的形成时代和过程对了解金沙江发育及区域环境演化具有重要意义。对龙街粉砂层空间分布及沉积特征进行野外调研,选择龙街、白泥湾、江头和白马口4个露头剖面采集样品,共采集剖面116m。其中龙街剖面出露地层40.6m,顶部与上覆河流相砂砾石层不整合接触,未见底；白泥湾剖面厚度40m,底部与元谋组角度不整合接触,上覆红色风化层；江头剖面和白马口剖面位于金沙江河谷,江头剖面厚度29.4m,顶部为红色风化层；白马口剖面厚6m,上部为金沙江阶地砂砾石层。通过龙街钻孔,获取了完整的龙街粉砂层沉积地层序列,合计厚度为101.18m,其中包含上覆的河流相阶地砂砾石层以及下伏角砾粗砂层。龙街粉砂层与上下地层之间均为不整合接触关系。通过龙街、白泥湾、江头、白马口剖面和龙街钻孔龙街粉砂层的磁性地层学、光释光、碳同位素年代学研究,认为龙街粉砂层的形成时代约为151～30ka BP。对龙街粉砂层剖面及钻孔样品进行系统粒度组分及参数分析,认为龙街粉砂层为一套湖泊相沉积物,其沉积环境可分为成湖阶段(151～148.5ka BP)、湖泊扩张阶段(148.5～132ka BP)、深湖泊阶段(132～91.5ka BP)、湖泊收缩阶段(91.5～67.2ka BP)、浅湖阶段(67.2～39.4ka BP)及河湖交替阶段(39.4～30ka BP)6个主要沉积阶段。色度、有机碳及碳酸盐含量等代用指标分析结果表明,研究区15万年以来(151～30ka BP)的气候环境可分下5个主要阶段：温湿期(151～132ka BP)、暖湿期(132～91.5ka BP)、凉湿期(91.5-67.2ka BP)、干冷期(67.2～39.4ka BP)和干热期(39.4～30ka BP)。其中也记录了在约141.2ka BP的暖干突变事件以及约60～63kaBP、50kaBP、44ka BP的暖湿事件。研究区环境与全球气候变化有较好的同步性,也具有区域的差异性特征,116.5ka BP左右的急剧变冷、100～95ka BP更高升温幅度以及70～59ka BP暖干期等与全球变化存在一定差异。更多还原

【Abstract】 The Longjie silt stratum is a series of silt, silty clay and clay horizontal layers, whose color contains grayblack, luidity and gray. It distributed along the valley of Jinshajiang River from Sanduizi of Panzhihua City to Baimakou of Wuding County, and well-developed in the Longjie basin in Yunnan Province. The formation age and process of the Longjie silt stratum will be importance in the research of the evolutionary process of Jingshajiang River and the regional tectonic activities.Based on the systemic field survey, the Longjie, Bainiwan, Jiangtou and Baimakou natural stratigraphic profiles have been collected, and these four profiles is about116m thick altogether. The Longjie profile is40.6m thick, it is showed the parallel unconformable contact relationship between the top layer and the overlying fluvial sand gravel. The Bainiwan profile is40m thick and capped by the red regolith, there exited an angular unconformity between the Longjie silt stratum and its underlying Yuanmou Formation. The Jiangtou profile is29.4m thick and capped by the red regolith, Baimakou profile is6m thich and covered by the fluvial sand gravel.The relatively intact stratigraphic sequence has been acquired by the Longjie drill. Including the overlying fluvial sand gravel and the underlying coarse sand, the total thickness is101.18m, and the Longjie silt stratum is in unconformable contact with the overlying and underlying layers.Through the study of the magnetostratigraphy, OSL and14C dating work, it is showed that the formation age of Longjie silt stratum is about151-30ka BP.The analysis of grain size indicated that the Longjie silt stratum was a set of lacustrine sediment, and its sedimentary environment could be mainly divided into6stages, which include the forming stage (151■148.5ka BP), lake expansion stage (148.5～132ka BP), deep lake stage (132±91.5ka BP), shrinking stage (91.5-67.2ka BP), shallow lake stage (67.2±39.4ka) and transformation stage (39.4±30ka BP).The regional climate and environment character form the151ka BP could be roughly divided into5periods, based on the study of climatic proxies which include chromaticity and carbon content. These5periods include the warm wet period (151±132ka BP), warmer wetter period (132～91.5ka BP), cold wet period (91.5～67.2ka BP), cold dry period (67.2±39.4ka BP) and warm dry period (39.4±30ka BP). At the same time, through the analysis of regional climatic and environmental change process, the climatic proxies also indicated some climatic events, such as the warm dry event which occurred at about141.2ka BP and the relatively warm wet events that occurred at60±63、50and44ka BP. The climatic change of research area shows good synchronism with the global change in generally, but it also showed some regional differences:the rapid cold at116.5ka BP, the warmer at100±95ka BP and70±59ka BP.更多还原