东濮断陷湖盆下第三系沙二段的冲积扇沉积

Alluvial Fan in Paleogene Shahejie Formation, Dongpu Faulted-basin

东濮凹陷西洼南段沙二段是该区主要的勘探目的层之一。根据地震、测井及岩心分析等资料的综合分析表明，该区沙二段属干旱气候条件下的冲积扇沉积。由于沙二段沉积时期长垣断层的活动减缓，研究区与西斜坡构成一个共同的沉积区域，研究区内主要发育扇中前缘和扇端亚相等细粒沉积部分，扇根和扇中主体等粗粒部分主要堆积在西斜坡上。在地震剖面和测井曲线上可以看出，该区沙二段由３ 个沉积旋回构成，总体上呈现向上变细的粒序特征。这些旋回在研究区各井中可以进行对比，表明冲积扇的活动受构造和气候因素的影响。

The No.2 member of Shahejie Formation(Paleogene) is one of the major target beds in Dongpu depression. An investigation based on seismic, well-logging and core data indicates that the member consists of alluvial fan sediments in the southern west sag. The sediments are mostly brown-grey brown finer lithic arkose and coarse siltstone, interbedded with brown mudstone,with medium-low compositional and textural maturation.Some sedimentary structures, such as graded bedding, small-scale cross bedding, ripple lamination and horizontal bedding caused by density and traction flow deposition,and such as mud crack,burrow,swash mark and curty bedding caused by exposure and others, are seen in cores,and scatters are distributed along a line parallel to C=M line in CM plot.The features show that the sediments are deposited under the influence of density and traction flow.The study area is combined into a depositional unit with the West Slope because of a decrease of the boundary faults action in the depositional age of the member, resulting in finer-grained front middle-fan deposition in the study area and coarse-grained proximal fan in the West Slope of Dongpu depression. This is why the alluvial fan sediments of Es 2 member have finer grain-size in the study area. In seismic profiles and well-logging curves, three sedimentary cycles are recognized in the member, showing an fining upward trend. The cycles are correlated between wells in the area, indicating the control of tectonics and weather.