准噶尔盆地侏罗纪含铀岩系的层序划分与对比

为对比分析准噶尔盆地侏罗纪含铀岩系的特征,在盆地北部、东部、南部筛选了3个钻透中下侏罗统西山窑组(J_2x)和八道湾组(J_1b)的钻孔,以岩性组合、沉积特征和测井曲线为基础,结合层序地层学原理和前人研究成果,对其含铀岩系进行了划分与对比。选择12个铀矿化异常孔编制了层序沉积连井模式图,讨论了层序充填及演化特征。结果表明:盆地不同位置地层层序差异较大,北缘从侏罗系下统三工河组到侏罗系上统齐古组(J_1s—J_3q)发育了3个三级层序和7个体系域。盆地东缘从侏罗系下统八道湾组到上统齐古组(J_1b—J_3q),发育了5个三级层序和12个体系域,整体经历了一个较为完整的湖侵过程,4个次级的湖侵湖退使湖平面达到最高位。南缘从侏罗系中统西山窑组到上统齐古组(J_2x—J_3q)发育了3个三级层序和7个体系域,经历一次构造隆升作用造成了大规模湖退事件和一次完整的湖侵事件。八道湾期至齐古期至少经历了两次完整的湖退、湖侵事件,整体上经历了一个先退积、后进积、再退积的过程。头屯河期湖退过程中形成的扇三角洲、辫状河砂体是主要的铀储层,也标志着一次重要的构造隆升事件。研究区岩相主要有辫状河、辫状河三角洲、湖泊、湖泊三角洲和扇三角洲5种沉积相类型和10种沉积亚相,含铀岩系亚相主要有辫状河道、扇三角洲平原、湖泊三角洲平原。西山窑组(J_2x)含煤建造上下发育2个区域性平行不整合面,界面之下发育大规模湖泊三角洲相的粘土层圈闭了上下两侧的砂体,是寻找砂岩型铀富集的有利区带。这些认识,不仅提高了准噶尔盆地侏罗系层序地层的对比划分的精度,而且对盆地控铀要素和形成环境研究及全面开展铀矿找矿工作意义重大。

Classification and Correlation of Jurassic Uranium bearing Series in the Junggar Basin

In this paper, through the analyses of sedimentary rock assemblages, structures and logging traces of twelve wells respectively from the north, east and south margins of the Junggar Basin, have been studied for classification, correlation and sequence stratigraphic framework of Jurassic Uranium bearing Series. All researches indicate that the sequence stratigraphy have big differences in different positions. The sequence from Sangonghe Formation to Qigu Formation on the north margin of the Junggar Basin is three, including seven system tracts. The sequence from Badaowan Formation to Qigu Formation on the east margin of Junggar Basin is five, including twelve system tracts. And the sequence from Xishanyao Formation to Qigu Formation on the south margin of Junggar Basin is three, including seven system tracts. During the Badaowan and Qigu period, it had at least two lake formation. The whole experiences the process of retrogradation, progradation and then retrogradation again. Alluvial sand bodies of braided stream and delta fan are the main uranium reservoir. And the delta fan on the north margin also indicates uplifting events. The Jurassic in the study area mainly developed five kainds of deposition types, which are braided, braided viver deltas, lakes, lake deltas and delta fan, ten kinds of sedimentary subfacies types. The subfacies types of uranium bearing series are braided channel, fan and lake delta plain. There were two parallel unconformities respectively up and under the coal bearing formation of Xishanyao period. The clay ground under the unconformaities have formed stratigraphic trap, the sand bodies on the two sides of the unconformaities are the most favorable exploration targets in the Junggar Basin. All the above results not only provide new constraints on increasing the precision of classification and correlation of Jurassic Uranium bearing Series in the Junggar Basin, but also have great significance on the exploration of sand type uranium.