【作者】 杨文光；

【导师】 朱利东；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2005， 硕士

【摘要】 新生代的青藏高原强烈隆升对高原的周边地貌产生了显著影响,也同样影响了青藏高原周缘的水系演化历程。沉积盆地与河流阶地的沉积特征不但记录了盆地或阶地的水动力条件和沉积物来源,也记录了区域性的构造活动与气候变化。岷江位于青藏高原东缘,在岷江上游流域发育有多级河流阶地,其中三级阶地的分布范围广、发育规模大,为此通过对岷江上游叠溪与茂县两地的三级阶地及相关沉积的沉积学特征讨论,以及成因分析和区域对比研究,将为探讨青藏高原东缘的构造活动与气候变化过程提供重要基础资料。 “沉积体系”是成因上相关的沉积环境及沉积体的三维岩相组合。沉积体系的分析需要做大量的二维或三维的观察,在沉积组合的划分和成因分析上客观适用,因而被众多沉积学家接受和广泛应用。岩性相,是Miall(1978)在研究河流碎屑沉积时提出的概念,它是以岩性和其具有的沉积构造划分出来的最基本的岩相类型。岩性相的识别和划分是进行沉积体系野外描述的一种简便的、较为客观的方法。 本文在以岩性相为手段的野外调查基础上,采用沉积体系分析的方法,探讨了岷江上游茂县和叠溪两个地区的沉积演化历史、构造与气候变化历史,得出以下主要认识: 1) 叠溪研究区主要发育河流沉积体系、湖泊沉积体系、冲积扇沉积体系、风成沉积体系以及古土壤层,位于堰塞湖的库尾;茂县研究区主要发育河流沉积体系、扇三角洲沉积体系、风成沉积体系。其中扇三角洲沉积体系又分为三个成因相组合:前扇三角洲组合、扇三角洲前缘组合和扇三角洲平原组合,位于堰塞湖较深处,有可能是近湖心。 2) 叠溪研究区堰塞湖启动时间为10.7万年,结束时间为6.2万年。茂县研究区堰塞湖的发育时限与叠溪大致相当。叠溪和茂县两个研究区都是古堰塞湖消亡以后,堆积了风成黄土。在隆升构造影响下,河流下切,形成三级阶地。 3) 叠溪研究区湖相沉积中出现了古土壤,属于暴露成因,预示叠溪地区至少发育两期滑坡堵江与溃堤事件。古土壤的特征与发育也预示着当时的气候为湿热。 4) 黄土的年龄为6.2万年,黄土的风成成因说明6.2万年左右岷江上游气候干冷。黄土剖面中出现了古土壤层,说明在风成黄土形成过程之中气候出现了干冷—湿热—干冷的变化过程。 5) 10.5万年左右,多起滑坡堵江事件的出现,预示着岷江上游当时处于构造活动强烈期。结合6.2万年左右风成黄土的堆积,可能预示着在10-6万年之间发生了快速隆升,并导致区域气候的变化。更多还原

【Abstract】 The intensive uplift of Qinghai-Tibet on the Cenozoic era has great effect on landform and the water system evolution of the marginal area. Depositional records in the sedimentary basin and river terrace not only mark the hydrodynamic force condition and the origin of deposit, but also record the local tectonic activity and the climate changes. The Minjiang River is situated in the eastern margin of the Qinghai-Tibet, where exists multilevel river terraces in the upper reaches, especially terraces III distributing widely and developing largely. This thesis pick up the terraces III of Diexi and Maoxian to make researches in sedimentary. It discusses about the tectonic activities and climate changes of the eastern margin of the Qinghai-Tibet, on the base of genesis analyses and regional contrast."Depositional system" is 3-D lithofacies unit of depositional environment and sedimentary body, which are originally related. Analyzing of depositional system needs more 2-D or 3-D survey.The method of depositional systematical analyzing is applicable to sedimentary unit dividing and genesis analying, so it is widely accepted and extensively applied by numerous workers. Lithofacies, the most important concept in the depositional system, was put forward by Miall (1978) when he studied the potamoclastic deposit. It is the basic type of lithofacies which was divided according to lithology and its sedimentary structures. Lithofacies discernment and division is a simple, convenient and comparatively objective method in the field description of depositional system.Based on field investigation of lithofacies, this paper discuss the sedimentary history and tectonic and climatic history in the two research areas of Diexi and Maoxian in the upper reaches of Minjiang River by using the method of depositional system analyzing. The results are giving just as following:a) Diexi study district which should be located in the end of barrier lake, mainly developed fluvial depositional system, lake depositional system, alluvial fan更多还原