Study on Modern Deposit of a Braided Stream and Facies Model-Taking the Yongding River as an Exampl e
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摘要: 永定河是一条多河型河流,自上而下,包括了辩状河→曲流河→分流网状河的河型空间转换。其间辫状河段可明显区分为两类亚型:即冲积扇区的高坡降辫状河和冲积平原区低坡降辫状河。二者在河流形态、沉积物特征等方面显示不同。而沉积作用机制和砂体沉积模式是近似的,二者均进行垂向加积作用,均发生五个级次的沉积再作用面,均发育三个级次类型的薄夹层:滞留层、落淤层、颗粒降纹层与颗粒流纹层。其中落淤层最具指相意义。在河道经常摆动迁移过程中,最终形成砂体广泛展布的“叠覆泛砂体”。这种辫状河沉积模式──“叠覆泛砂体”为油气储集提供了良好的储集空间和场所。Abstract: There are multipatterns in the Yongding River and they transfer from the braided to meandering,then toan abranched channel along the flow direction. The braided stream segment can be subdivided into two types:One is a high slope braided river which is distributed in the fluvial fan,water escaping,gravitational sliding,water flow dragging,ripple gliding,bioturbation,wave action and slump-ing,and can be divided into seven types according to their origins. Those formed by water escaping and waterflow dragging are the most common and typical ones among them. On surfaces of the deformed beddings of water escaping type,there are usually many nipple-like and do-ral fin-like projectings which may sometimes have a hole for water escaping in the center of each projecting,and the deformed beddings may have abrupt contact with their neighbor beddings. Deformed beddings of wa-ter flow dragging type usually possess five characteristics as follows: (1)the overlying sedments and sedimentary structures of them,such as clay boulder or sand-sized grainsin massive and parallel beddings,regressive sand waves,climbing-ripple laminations, are all formed by waterflow of high velocity. (2)the axial planes of fold curve-like deformed beddings are often randomly oriented,al-though they may sometimes dip toward the upper reach. (3)usually,they show abrupt contact with overlyingbeddings and gradual or abrupt contact with underlying beddings of them according to extent of deformation.(4)most of them are deformed severely and show very complicated appearences such as the cabbage-like onesand the bag-like or tube-like ones. (5)they are steadily widespread and sometimes may be well-stratified andgraded.
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Key words:
- deformed bedding /
- delta /
- Yellow River /
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