内蒙古二连盆地白音查干凹陷热水沉积序列探讨

近年来在内蒙古二连盆地白音查干凹陷下白垩统发现一套夹于深-半深湖相泥岩中，富含泥级钠长石、铁白云石、钠沸石、水镁铁石、重晶石等特殊矿物成分的热水沉积岩。该套岩石测井曲线上显示出异常高的自然伽马（G_R=700~1 100 API），为正常泥质岩自然伽马值的2~4倍，电阻率出现特高（2 000 Ω·m）-特低（0.2 Ω·m）的剧烈变化。根据热水沉积岩的岩石学特征，通过多口单井岩芯的详细解剖，结合相应的测井响应特征，可将腾格尔组-都红木组的热水沉积岩划分为四个旋回，每一旋回呈现低自然伽马值岩性段--尖峰状高自然伽马值岩性段特征，所对应的岩性序列可将热水沉积过程划分为三个阶段:初期为热液溢流期，主要在正常湖相泥岩中形成白云石及沸石纹层、条带或夹层，相应的岩石为低自然伽马的白云质沸石质泥岩；随后随着热液活动增强，出现喷流，使初期溢流形成的半固结白云石沸石纹层发生变形破碎，形成具有同生变形构造的白云质泥岩、白云石沸石内碎屑颗粒岩，测井曲线上仍然显示为低自然伽马特征；最后由于热液活动能量衰减，再次进入缓慢溢流阶段，形成高自然伽马泥质白云岩及部分白云质泥岩。

Discussion of Hydrothermal Sedimentary Sequence in Baiyinchagan Sag of Erlian Basin,Inner Mongolia

The lower Cretaceous hydrothermal sedimentary rocks had been found in Baiyinchagan sag of Inner Mongolia Erlian basin in recent years. The hydrothermal sedimentary rocks were rich in special minerals including clay sized albite, ankerite, natrolite, franquanite, barite, etc., and were only developed in semi-deep to deep lacustrine facies. The hydrothermal sedimentary rock can also be characterized by its log response with extremely high GR(GR=700~1 100 API), which is 2~4 times that of natural gamma value of normal argillaceous, and remarkably fluctuation in resistivity logging from as high as 2 000 Ω·m to 0.2 Ω·m. By the petrologic characteristics of the hydrothermal sedimentary rocks,the detailed analysis of single well core,combined with the corresponding logging response features, four hydrothermal actives can be recognized in Tenggeer-Douhongmu formation in the study area. One hydrothermal process will form a low natural gamma value lithologic section-the peak shape high natural gamma value cyclic deposition. A complete hydrothermal process consists of three stages: ①Early overflow process which precipitate low GR dolomitic or zeolitic fine grain rock with dolomite and zeolite laminae, zebra or interface layer. And ②Jet flow process with increasingly active hydrotherm. The laminae or interface layer of dolomite and zeolite will be deformed or even disrupted and result in dolomitic fine grain rock and clastic rock consisting of dolomitic or zeolitic intraclasts. After the energy of hydrotherm exhausted the hydrothermal activity will return back. ③Sluggish overflow stage and results in argillaceous dolomite rock and partial dolomitic mudstone with extremely high GR response.