岩石学观察和X射线衍射分析表明,伊利石是鄂尔多斯盆地东北部地区上古生界太原组砂岩储层中分布最广、含量最丰富的黏土矿物.显微观察识别出下述几种类型的伊利石:碎屑伊利石、具蒙皂石转化特征的伊利石、交代长石的伊利石、具高岭石过渡形貌的伊利石以及其他的自生伊利石.根据研究区太原组浅海沉积背景以及砂岩样品的组构、矿物学特征,认为一部分伊利石的成因与浅埋藏开放体系中大量外部来源的钾有关.而太原组砂岩中高岭石在数量上的缺失以及相关的岩相学特征则表明大部分伊利石应来自于深埋藏条件下钾长石与高岭石之间的反应.该过程是受到热力学与动力学控制的,早成岩期高K+/H+活度比的流体对钾长石的保存、伊利石化作用发生前长石向高岭石的转化以及相对较高的地层温度是其重要的控制条件.%Optical microscopy, XRD, SEM analyses on core samples from Taiyuan Formation of the Northeast Ordos basin has been performed. The results show that these sandstones are illite-rich. Several types of illite have been identified by petrological observations; detrital, smectite-transitional form, as replacement of feldspars and pseudomorphs after kaolinite. An external source of K+ supplied by marine-derived fluid can promote illite crystallization during early diagenesis, having cogenetic illite and K-feldspar crystals preserved in strata. However, petrographic evidences indicate that most authigenic illite in Taiyuan Formation possibly originated from the illitization of kaolinite at the expense of K-feldspars during late diagenesis. Kaolinite contents are deficit in Taiyuan Formation support this conclusion. This process is thermodynamically and kinetically controlled. (1)K-feldspar preserved by diagenetic fluid with high K＋ /H+ activity ratio at shallow depths, (2)kaolinite formed by feldspar dissolution before illitization together with (3) increasing temperature controls this burial illitization process.
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