Study on Modern Deposit of a Braided Stream and Facies Model-Taking the Yongding River as an Exampl e

Key words: 
• deformed bedding /
• delta /
• Yellow River /
•  /

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.