鄂尔多斯盆地西缘奥陶系拉什仲组复合水道沉积特征及演化

鄂尔多斯盆地西缘奥陶系拉什仲组发育一套砂泥互层的深水重力流沉积，其下部重力流复合水道发育。综合野外实测、薄片和粒度分析等，探讨复合水道沉积特征、形成过程及主控因素，最终建立其沉积模式。结果表明：(1)研究区发育5种岩相和3种岩相组合，即块状层理砾屑灰岩相(Cm)、粒序层理细—粉砂岩相(Sg)、平行层理砂岩相(Sp)、交错层理粉砂岩相(Sc)、水平层理(泥)页岩相(Sh),分别代表碎屑流沉积(Cm)、浊流沉积(Sg, Sp, Sc)及深水原地沉积(Sh);(2)根据复合水道内部单一水道形态、岩相组合及粒度等将复合水道分为4个期次，反映重力流能量由强到弱的变化过程；(3)复合水道多期次发育与相对海平面升降、沉积物供给、构造运动和重力流规模及能量变化密切相关；(4)重力流沉积为斜坡—盆地环境中复合水道沉积模式。该研究可补充对研究区重力流水道认识，为油气勘探提供借鉴。

Characteristics and evolution of complex channel in the Ordovician Lashizhong Formation in western margin of Ordos Basin

A set of deep-water gravity flow deposits with sand-mud couples are developed in the Ordovician Lashizhong Formation in the western margin of the Ordos Basin,and the gravity flow complex channel is developed in the lower part. Based on field measurement,microscopic observation and grain size analysis,the sedimentary characteristics,process and main controlling factor of complex channel are discussed,and finally the sedimentary models were established. The results show that: (1)Five lithofacies and three lithofacies associations are developed in the study area,namely massive bedding calcirudite lithofacies(Cm),graded bedding fine-siltstone lithofacies(Sg),parallel bedding sandstone lithofacies(Sp),cross bedding siltstone lithofacies(Sc) and horizontal bedding(mud)shale lithofacies(Sh),indicating debris flow deposits(Cm),turbidites(Sg,Sp,Sc) and deep-water autochthonous deposits(Sh). (2)According to the morphology,lithofacies association and grain size of single channel,the complex channel is divided into four stages,reflecting a gradually decreased gravity flow energy. (3)The multi-stage filling and evolution of complex channel are closely related to relative sea-level change,sediment supply,regional tectonic activities and gravity flow size and energy change. (4)The gravity flow sedimentation in the study area is a complex channel sedimentary system formed in a slope-basin environment. This study can improve the understanding of gravity flow channel in the study area and provide reference for oil and gas exploration.