准噶尔盆地玛湖凹陷百口泉组典型微相砾石定向性定量研究

A Quantitative Study on the Gravel Orientation of Typical Sedimentary Microfacies in Baikouquan Formation,Mahu Sag,Junggar Basin

砾石定向性可用于辅助判断粗粒沉积物沉积环境的介质性质与强度。在岩芯图像分析与测量的基础上,运用砾石长轴相对视倾角玫瑰花图中任意相邻三个小扇形的半径之和的最大值(参数a)和小扇形半径大小偏离程度(参数σ),对玛湖地区百口泉组152种典型砾岩岩石相以及四种典型微相中的砾石定向性进行定量研究,结果表明:玛湖地区百口泉组不同岩石相中砾石定向性存在一定的差异,但是总的来说岩石相中包含交错层理属性、平行层理属性、小中砾岩属性的,砾石定向性比较好,定向性参数比较大;四种典型微相中,辫状河道沉积、水下分流河道沉积、河口沙坝沉积中砾石定向性变化在垂向上都有一定的旋回性,而泥石流沉积中砾石定向性变化在垂向上的旋回性不是很明显;四种典型沉积微相中砾石定向性参数大小也存在一定的差别。定向性由差到好依次是泥石流微相(σ最大值为6.61、最小值为3.00、平均值为4.03,a最大值为52.94%、最小值为22.95%、平均值为32.87%)、辫状河道微相(σ最大值为8.91、最小值为3.11、平均值为5.31,a最大值为65.79%、最小值为25.93%、平均值为341.41%)、水下分流河道(σ最大值为7.22、最小值为2.96、平均值为5.11;a最大值为55.71%、最小值为25.93%、平均值为38.76%)、河口沙坝微相(σ最大值为10.34、最小值为3.65、平均值为5.54;a最大值为83.02%、最小值为32.35%、平均值为44.42%)。

Gravel orientation can be used to judge the environment of coarse grain deposits. On the basis of the analy-sis and measurement of the gravel image from the core image, using the parameters a and σ to study the 152 typestypical conglomerate lithofacies and four typical sedimentary microfacies of characterization of gravel orientation in theBaikouquan Formation sandstone in the Mahu sag. The parameter a is the maximum value of the sum of the radius ofthe gravitational axis of any adjacent three small fans, parameter σ is the degree of deviation of the small fan radius.It is found that the larger the a and σ is, the better the orientation of the gravel is; There are some differences in theorientation of different lithofacies and sedimentary microfacies in the Baikouquan Formation in the Mahu area; the ori-entation of lithofacies with the cross-bedding, the parallel bedding and the small conglomerate attribute is better, theorientation parameter is relatively large. The orientation characteristics show that vertical rotation of the braid channel,the underwater distributary channel and mouth bar are apparent, but the debris flow microfacies’s is vague. The sizeof the orientation parameters exist a difference in four typical sedimentary microfacies, the orientation is poorly fol-lowed by debris flow microfacies （σ has a maximum value of 6.61, a minimum of 3.00, and an average of 4.03; a hasa maximum value of 52.94%, a minimum of 22.95%, and an average of 41.41%）, braided channel （σ has a maxi-mum value of 8.91, a minimum of 3.11, and an average of 5.31; a has a maximum value of 65.79%, a minimum of 25.93%, and an average of 32.87%）, underwater distributary channel （σ has a maximum value of 7.22, a minimumof 2.96, and an average of 5.11, a has a maximum value of 55.71%, a minimum of 25.93%, and an average of32.87%）, mouth bar （σ has a maximum value of 10.34, a minimum of 3.65, and an average of 5.54, a has a maxi-mum value of 83.02%, a minimum of 32.35%, and an average of 44.42%）. We can use these differences to deter-mine different sedimentary microfacies.