Modern Channel Islands Deposits in Jingjiang Reach of Yangtze River

Channel island is a kind of fluvial topographical unit that is different to channel bar and side bar in river channels. Most of them developed in anastomsed rivers. Five of the seven channel islands in Jingjiang reach of Yangtze river have been investigated. The largest one has an area of 6.17km~2 and the smallest one has an area of 0.66km. Lengthes range from 6.9km~2 to 2.70km and width from 1.98km to 0.34km. Sediments are fining downstream island by island and for every of them from the fore to the tail. There groups of lithofacies distribute at different parts of a channel island. Gravel facies including Gm, Gt, Gp are dominated at the fore of channel island; Sandy facies including St, Sr, Sp, Sn, Si are mainly developed at the middle of channel island; Fines including Fi, Fm are found at the tail of channel island Two facies-assemblage G-S-F and S-F are found vertically. The word" Upper Channel Island Sequence" has been proposed by the author to describe the stratification situated at the top of channel island. Within the upper channel island sequences, fines are 70. 17% in thickness and 62.5% in unit-numbers, sands are only 27.3% in thickness and 33.3% in unit-numbers. Merely gravel unit has been discovered in the channel island. Frequences of sedimentary structures are distributed as: ripple laminations 23.3%, horizontal laminations 35%, parallel bedding 6.5 massive bedding 8.4%, rootlite and burrows are 9.3% and 7.4% respectly. A few of tabular beddings are discovered on these sequences. Four types of three dimension (3D) architecture elements including 1) NDA. 2) DAC 3) LABB and 4) UA are concluded to constitute the 3D architecture of an channel island sandbody.