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鄂尔多斯盆地长8段为浅水三角洲沉积,其沉积特征与典型的Gilbert三角洲有所不同。主要利用测井、岩心和薄片等资料,重点分析了姬塬地区长81砂体的物源搬运距离、物源补给量大小以及湖水水体性质、水动力条件等,确定了姬塬地区长81砂体沉积环境和形成条件。分析认为姬塬地区长81砂体距离物源区较近,物源供给稳定且较为充足;研究区长81期湖水水体浅且为微咸水,湖盆底部形态平缓,属于浅水三角洲沉积环境,其中,在长81期基准面上升过程中,湖水强势扩张使得湖水扩张动力大于河流入湖动力。姬塬地区长81沉积期,在物源补给量稳定且较为充足、湖水扩张动力强于河流入湖水动力的条件下,砂体受到湖水强烈的顶托作用,使砂体被动提前卸载,于是形成了垂向叠加期次不明显、纵向延伸距离长且连续性好的“连续退积式”厚层砂体。
The Chang 8 member of the Ordos Basin is a shallow-water delta deposit with sedimentary features different from the typical Gilbert Delta. Mainly using the well logging, core and thin-sheets and other data, the author focused on the analysis of the material source transport distance, the size of the material source, the nature of the lake water and the hydrodynamic conditions of the long 81 sand body in the Jiyuan area, Body sedimentary environment and formation conditions. The analysis shows that the 81-year body of the Chang 81 sand body in Jiyuan area is relatively close to the provenance area, and the source of the provenance is stable and adequate. The 81 lake water bodies in the study area are shallow and brackish, and the bottom of the lake basin is gentle and belongs to the depositional environment of shallow water delta. Among them, during the rise of the 81th datum, the strong expansion of the lake made the driving force of the lake water expand more than that of the river into the lake. In the Jiyuan area, during the depositional period of 81, under the conditions of stable and adequate supply of source materials and stronger dynamic expansion of the lake water than that of rivers, the sand body is strongly jacked up by the lake water and the sand body is passively unloaded in advance, thus forming The vertical superimposed period is not obvious, the longitudinal extension of the long distance and good continuity “continuous retrograde ” thick sand body.