【摘要】 对四川理县杂谷脑"冰碛物"的地层结构进行了观察,对河湖相地层中的软沉积物变形构造进行了分析。综合研究表明,所谓杂谷脑晚更新世"冰碛物"是由泥石流、崩滑塌堆积物、堰塞湖沉积和河流相砂砾石层构成的多成因"混杂"堆积,湖相地层中发育的强烈褶皱和断裂是河岸陡壁岩石崩塌滑落导致古堰塞湖沉积物发生软沉积变形的结果。软沉积变形构造包括卷曲构造、液化泥块、阶梯状微断裂、球枕构造、火焰构造、落石沉陷构造、环状构造、同生断层和大型褶曲等。一次崩滑塌事件的典型沉积层序由崩塌体、不规则接触面和下伏的河湖相变形地层所组成。沿杂谷脑河上游发现的一系列大型崩塌褶曲构造以及伴生的多种典型的液化变形构造,指示可能是地震活动触发了群发性的崩塌、滑坡灾害事件。更多还原

【Abstract】 The existence of Pleistocene glaciers at altitudes lower than 3000m in the East Tibetan Plateau is still a matter of debate and requires further studies based on sedimentary features. In the Zagunao area,unconsolidated sediments mainly composed of boulder clay and laminated layers were firstly reported in 1964 as moraines of the last glaciations,and intense folds and faults in the sediments were believed to be deformation caused by glacial processes. However, the same sediments were also recognized as a mixture of debris flows, glacial varved clay, fluvial deposits,and colluviums. The Zagunao River,the largest tributary in the upper reaches of the Min River,is originated from the east lope of the Qionglai Mountains and runs into the main stream at Wenchuan ,the center of the MsS. 0 earthquake occurred on May 12, 2008. This area belongs to the Western Sichuan and is located at the east edge of the Tibetan Plateau in an active earthquake region, known as the Longmenshan Fracture Zone. The representative section of the sediments is located at about 1 km upstream from the Lixian County,the Zagunao Town with an elevation of 1909m at the highest point. Based on careful observation of the sedimentary textures and structures of the so-called moraines, the components of the section are identified as a complex assemblage of different facies including debris flows, colluvial deposits, fine grained lacustrine sediments of dammed paleolakes and fluvial sand and gravel layers. The deformational structures of different scales are discovered mainly in the lacustrine layers and can be sorted as hydroplastic deformation, liquefied mud, fault grading, ball-and-pillow structure, flame structures, dropstone structure,loop beddings, synsedimentary faults and folds, etc., which are typical deformational structures in seismites. The lacustrine layers in the Zagunao section are overlaid by massive colluviums which were formed by large landslips or collapses from the bank cliff. Adjoining the uneven contact beneath the colluviums are big intense folds in the lacustrine layers with their axial planes dipping to the collapses. Thus,heavy impact or sudden compaction from big collapses other than glaciers is a more reasonable explanation for the formation of these folds and some of the accompanied liquefied deformational structures. As most of the deformations occurred in the soft lacustrine deposits,it can be inferred that a dammed lake existed when the collapse took placed. In addition, dammed lake deposits are widely distributed in many places along the Zagunao River upstream from Lixian, and similar deformational structures can be found accompanied with colluviums. By integrating both the collapses and deformation structures together, there is no sufficient evidence for the existence of glaciation here and it is logical to infer that the congregating of collapses in different forms and at different localities in the river valley indicates a sedimentary event which may be induced by seismic activities in the past. Therefore, the establishment of a sedimentary sequence composed of colluviums, uneven contacts, and deformed fluvial and lacustrine formations as a representative type of seismite in dammed paleolake have an important significance for the study and reconstruction of historical earthquakes in this region.更多还原