鄂尔多斯盆地西北部下石盒子组盒8段(简称:盒8段),整体具有构造稳定、沉降缓慢、盆大、坡缓、水浅、源多的特点,广泛发育缓坡型浅水辫状河三角洲沉积.运用地层过程-响应沉积动力学原理和高分辨率层序地层学的理论及方法,对该类三角洲砂体的成因与组合类型进行了探讨.该时期砂体明显受基准面升降旋回过程中可容纳空同和沉积物补给通量比值变化的控制,可划分为进积型、加积型.进积型主要由高能削截武河道砂体、低能削截式河道砂体、残缺式埙上河砂体构成;加积型则主要由低能削截武河道砂体、完整式河道砂体、下残式坝上河砂体构成.结合砂体的时空展布规律,建立了缓坡型浅水辫状河三角洲砂体成因分布模式.层序界面上的高能河道砂体富集岩性油气藏,勘探潜力大.%Member 8 of Lower Shihezi Formation in the northwest of Ordos Basin is characterized by the regional tectonic setting with steady and slow subsidence, large area, gentle slope, relatively shallow water and multiple sources. The gentle slope-type shallow braided river delta is developed. The author takes the stratigraphic and sedimentary process-response dynamic principles as a theoretical basis, and uses the theory and technology of the high-resolution sequence stratigraphy to explore the genetic combination types of this kind of delta sandbodies. The sandbodies were evidently influenced by the relation between accommodations and sediment alimentations during the base-level up and down changes. The sandbodies in Member 8 consists of two vertical superposed types of progradation model and aggradation model from bottom to top. The progradation model mainly includes high-energy truncation style channels, low-energy truncation style channels, and deformity recombination which mouses bars at the bottom and under water distributary channels at the top; The aggradation model mainly includes low-energy truncation style channels, complete channels, downside deformity recombination which mouses bars at the bottom and under water distributary channels at the top. On the basis of the above analysis, the high energy channel sandbodies on the sequence boundary are abundant in lithological reservoirs in the delta plains which show the great potential for oil and gas exploration. Consequently, The genesis and distribution pattern of sandbodies in a gentle slope-type shallow braided river delta is established based on the spatial-temporal distribution of the sandbodies in Member 8 of the study area.
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