【摘要】 湖盆可容空间较小时 ,辫状河三角洲相对发育 ,水下分支河道横向迁移频繁 ,易形成席状分布的砂体 (水下分支河道复合体 )。可容空间增大时 ,辫状河三角洲相对不发育 ,水下分支河道延伸不远 ,河道砂体较孤立 ,河口坝相对比较发育。文中根据水流和波浪强弱提出九种水下分支河道与河口坝的关系图 ,基本上总结了吐哈盆地WM油田三间房组河口坝的形态 ;并对水下分支河道复合体的形成机制提出了独特的推理更多还原

【Abstract】 The braided delta front is developed in WM oilfield, Turpan-Hami Basin, which is composed of the underwater distributary channels , mouth bars, distal sands, sheet-like sands, and interchannel muds microfacies. The deposition features of the braided deltas are low sedimentary maturation and abundant current structures caused by the traction current. The underwater distributary channels have an erosion surface in the channel bottom, and are fining upward from conglomerates in the base to fine-sandstones in the top of the channels. They are 2.5m in rhythm, and 4～10 m in complicate rhythms , and are 200～400 meters in width. The parallel bedding are well developed in the sandstones. While the mouth bars are coursing upward from siltstones to sandstones, and are large than 4 m in thickness. The sheet-like sands are mainly sandstones, fine to medium grained, well sorted and rounded, and are mostly coursing upward. They are 3-4m in thickness. The rivers in the braided delta are strong, so that the distributary channels still erode downwards after entering lake ,and forms underwater distributary channels as a result of water flow in the bottom of the lake, The underwater distributary channels can frequently migrate laterally so as to form sheet-like sandbodies (complicated sandbodies of the distributary channels). Some uneroded interchannel muds are scatterd in the inner of complicated sandbodies of the distributay channels, and will be flowing barriers. The volumes of the mouth bars depend directly on the amounts of sediments carried by underwater distributary channels ,while the shapes are partly influenced by the waves of the lake. The mouth bars may be ellipsoid parallel to underwater distributary channels (i.e. perpendicular to the shore of lake),but may become fan-like and even ellipsoid parallel to the shore of the lake by the modification of the waves. The nine kinds of relationship between the underwater distributary channels and the mouth bars are proposed according to the strength of the currents in the distributary channels and the strength of the waves in the lake. It has concluded the shapes of the mouth bars in the Sanjianfang Formation, WM Oilfield, Turpan-Hami Basin. The underwater distributary channels of next stage may flow by the franks of the former mouth bars and develop forward; as a result ,the mouth bars are presented along with the franks of the underwater distributary channels. The underwater distributary channels of next stage, however, may flow on the top of the former mouth bars and erode them. They may cut part of the mouth bar deposits and may form composed sand bodies of the mouth bar (upper) and underwater distributary channel (lower) if erosion is weak. They way cut all the mouth bar as the latter is never presented if the erosion is strong and the former mouth bar is too thin. A kind of thin-beded, fine-grained , lenticular sand bodies, which is called distal sands microfacies in the paper, is deposited in inter bars, shallow lakes in the weak wave region by the reworking of deposits of the mouth bars and underwater distributary channels by the weak waves or other currents in the lake. However, in the region of strong waves, the sediments of the underwater distributary channels and the mouth bars are by strong waves and migrated laterally to form continuos, large scaled sheet-like sands. When the accomodation space of the lake basin is smaller, the braided deltas are well developed, and inter channel mud deposits are eroded by the underwater distributary channels in braided deltas, so as to form sheet-like sandbodies (complicated sandbodies of the distributary channels). When the accomodation space of the lake basin is larger, the braided deltas are less developed, and the underwater distributary channels can not stretch too far away and channels sandbodies are much more isolated, while the mouth bars are relatively more developed.更多还原