鄂尔多斯盆地西缘奥陶系拉什仲组深水水道沉积类型及演化
The Type and Evolution of Deep Water Channel Deposits of the Ordovician Lashizhong Formation in Western Margin of the Ordos Basin

深水水道沉积是深水区重要沉积类型之一，对其形成机制研究不仅能提高深水沉积认识，还能为油气勘探提供帮助.以露头资料为基础，对鄂尔多斯盆地西缘奥陶系拉什仲组深水水道形成机制进行了详细研究.拉什仲组岩性以灰绿色页岩及砂岩为主，另见少量的粉砂岩及砾岩.槽模、交错层理、粒序层理及变形构造等发育.总体反应深水沉积环境，重力流沉积较为发育.其中，深水水道沉积极为典型.根据形态、结构及沉积方式等，将研究区深水水道沉积划分为了限制型和非限制型水道沉积.前者包括复合型及垂向加积型水道沉积，后者由迁移型及孤立型小水道沉积组成.复合型水道沉积厚约7.5 m，岩性以粗砂岩为主，底部见砾岩，水道轴部沉积、次级水道及水道－堤岸复合体沉积发育，可分为早期、中期和晚期.垂向加积型水道沉积宽为12.4 m，厚为1.3 m，宽深比为9.54，以中砂岩及细砂岩为主，水道内部以层状砂岩充填为主.迁移型水道沉积宽为6.9～ 12.3 m ，厚为0.23～0.73 m，宽厚比14.11～53.48，以中－细砂岩为主，具有明显的北西向迁移特征；孤立型小水道沉积宽为 0.5～ 0.6 m，厚为0.15～0.25 m，宽厚比为2.4～3.33，多为细砂－粉砂岩组成，透镜状，规模小.重力流爆发初期，能量高，侵蚀作用强，发育复合型及垂向加积型水道沉积；重力流中－后期，能量逐渐降低，迁移型水道沉积开始发育；当重力流后期及末期时，其能量进一步降低，发育孤立型小水道沉积.而在空间位置上，复合型及垂向加积型水道沉积多发育在斜坡中上部，中部及下部发育迁移型水沉积道，斜坡脚及深海盆地以孤立型小水道沉积最为发育.
The deep-water channel deposits is one important sedimentary type in the deep-water zone. Research on the mechanism of deep-water channel is not only improve acquaintance of deep-water deposits, but also is helpful to oil and gas exploration. Mechanism of the deep-water channel of the Ordovician Lashizhong Formation in western margin of the Ordos basin was detailedly worked based on outcrop. The lithology of Lashizhong Formation consist of greyish-green mudstone and sandstone and few siltstone and conglomeration with flute cast, cross bedding, graded bedding and deformation structure, which suggests deep-water environment. Gravity flow deposits are well developed. The deep-water channel deposits are also typical. It is found in this study, the deep-water channel deposits could be divided into confined and non-confined channel, based on the morphology, structure, and sedimentary style. The former includes complex and vertical aggradation channels deposits. The latter can be subdivided into migrational channel and isolated small channel deposits. The lithology of complex channel deposits is coarse sandstone and conglomeration in the bottom, containing channel axis deposit, secondary channel and channel levee system deposits, with 7.5 m in width, which could be divided into developmental, mature and decline phases. The vertical aggradation channel deposits are bedded medium and fine sandstone, with 12.4 m in width, 1.3 m in thickness, and the width to thickness ratio of 9.54. The migrational channel is medium to fine sandstone with northwestward migration. The width is 6.9-12.3 m, the thickness is 0.23-0.73 m, and width to thickness ratios range from 14.11-53.48. The isolated small channel deposits consist of fine sandstone and siltstone, lenticular shaped, small scale with 0.5-0.6 m in width, 0.15-0.25 m in thickness, and the widthtothickness ratio of 2.4-3.33. The complex