新疆准东煤田西黑山勘查区中侏罗统西山窑组辫状河三角洲-滨浅湖沉积体系

The Braided river delta-Shallow lake depositional system of middle Jurassic Xishanyao Formation in the Xiheishan Coal District,Eastern Junggar Coal field,Xinjiang

准东煤田中侏罗统西山窑组(J2x)含煤岩系形成于大型陆相湖盆。应用现代沉积学理论,结合钻井岩心描述、测井等资料,详细研究了西黑山勘查区西山窑组的沉积特征,共识别出辫状河流、辫状河三角洲和湖泊3种沉积相类型的6种亚相,11种微相。研究表明辫状河三角洲沉积具有较高的砂泥比,发育厚层复合砂体,典型的河口坝沉积序列,以及各种河流-湖泊交互环境下形成的交错层理、砂泥复合层理,多见生物扰动构造和滑塌变形层理。辫状河三角洲沉积与湖泊沉积在垂向上交互,侧向上共生。区域性分布的厚煤层主要发育于废弃的辫状河三角洲朵叶之上和於浅的滨浅湖区。

The middle Jurassic coal-bearing Xishanyao Formation in the Eastern Junggar coal field,was formed in the large limnic basin.Based on the information from the drilling cores and well logs,depositional systems and coal accumulating regularity of Xishanyao Formation in the Xiheishan coal district are analysed.Three types of sedimentary facies,the braided river,the braided river deltas and the shallow lake,are recognized.In these sedimentary facies,6 subfacies and 11 mcrofacies are identified.The braided river deltas are mainly characterized by the very high sand/mud ratio,the thick sandstone assemblage,the typical mouth bar deposits,and the cross-beddings、bioturbation and slumping structures under braided delta-shallow lake conditions.The braided delta and the shallow lake sediments alternate vertically,and coexist laterally.Coal with great significance mainly developed on abandoned braided delta lobes and silted shallow lake.