印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析*

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。

Analysis on characteristics and formation process of sediment waves on the Pleistocene channel levee backslope of Indus fan

Architecture of the turbidity current sediment waves exhibit intricate morphologies and patterns on Indus fan channel levee back. The sediment waves are present on the channel levee of Pleistocene age in the study area,and their formation process is poorly understood. Through high-resolution seismic data and seismic interpretation technology, the difference between sediment wave and sediment deformation characteristics is expounded,and the distinguishing mark of the two sediments are summarized;the distribution law of sediment wave on the slope of the channel levee backslope and the regional slope is summarized;on this basis,the formation mechanism of the sediment wave is discussed,and the controlling factors and the formation process of sediment wave are analyzed. At last,the formation mode of sediment wave in Indus fan are established. The research result shows that: (1)The average wave length of the sediment wave in the study area is 486.84 m,and the maximum wavelength is 1473 m;the sediment wave height is between 10 m and 66 m,with an average of 30 m. (2)The morphology of sediment wave is symmetric and asymmetric,and its migration pattern include upslope migration type,aggregative type and downslope migration type. the sediment wave is mainly developed on the channel levee back,a small amount of sediment waves are also developed on the regional slope. The trends of these two types of sediment waves are very different. The sediment waves on the channel levee backslope are mainly distributed on the levee backslope in concave bank of the channel. The farther away from the channel,the smaller the dimension of sediment waves(wave length and wave height),and its trend is close to the NE-SW direction,parallel or oblique to the channel trend. The trend of sediment waves on the regional slope is mostly NW-SE,which is parallel to the trend of the regional slope,and its dimension is larger the farther away from the source area. (3)The sediment waves on the channel levee backslope is formed by the channel-type turbidity current overflowing the levee of the concave bank of the channel under the action of centrifugal force and depositing on the levee backslope outside the bank. The angle of the levee backslope have less effects on the dimension of the sediment waves. The intensity of turbidity current and the amount of sand conveying have a great influence on its dimension. The sediment waves developed on the regional slopes are formed by the non-channelized turbidity currents and are deposited along the slope,and it was considered that the undulating landforms caused by slump deformation,and the existence of early sediment waves all affect the development of later sediment waves.