准南水磨沟侏罗系喀拉扎组冲积扇沉积模式

The depositional characteristics and model of Kalazha formation in Shuimogou profile,Junggar basin

准噶尔盆地南缘水磨沟侏罗系喀拉扎组的沉积相类型尚不明朗,不同相带的岩相组合及具体沉积作用尚不清楚.在详细的实测剖面与露头观察描述的基础上,运用沉积学原理对水磨沟剖面中喀拉扎组地层由下至上岩相分异的成因进行了分析,研究后认为:1)准噶尔盆地南缘水磨沟剖面喀拉扎组为碎屑流与辫状河混合型冲积扇沉积,其主要建设性作用为重力流沉积作用与牵引流沉积作用;2)依据不同沉积作用所在的主要位置将冲积扇分为扇根、扇中和扇端3个亚相,扇根以碎屑流沉积作用为主,扇中以砂、砾混合质辫状河沉积作用为主,扇端以砂质辫状河沉积作用为主;3)喀拉扎组的岩相类型包括7种,剖面上部70m厚沉积以Gms为主,中部48m厚沉积以Gm与St,Sp,Sh组合为主,下部240m以St,Sp与Sh组合为主;4)造成喀拉扎组地层沉积序列向上变粗的本质原因为沉积物堆积速率大于盆地沉降速率,冲积扇沉积体不断向前堆积使近端相叠置在远端相之上.

Until now, there is no sufficiently identification of the sedimentary facies, lithofacies and depositional processes of Jurassic Kalazha formation in Shuimogou profile, south Junggar basin. Based on the detailed observation, description and measurement of the outcrop, the origin of lithofacies dif- ferentiation was analyzed using principles of sedimentology. The results show that： the sedimentary facies of Kalazha formation was an alluvial fan which is a mixed type of debris-flow and braided stream, and the alluvial fan is mainly formed by depositional processes of the sediment gravity flow and traction flow; （2） the alluvial fan is subdivided into three subfacies in terms of the location of dep- ositional processes, namely proximal fan, medial fan and distal fan, and the depositional process of proximal fan is debris-flow while the process of medial fan is gravelly and sandy braided stream and that of the distal fan is sandy braided stream; （3） the lithofacies of Kalazha formation include Gins, Gin, Gp, St, Sp, Sh, Mh, and the Gins represent deposits of debris flow which is in the 70-meter thick upper part of the profile, but the Gin, St, Sp and Sh represent deposits of gravelly and sandy braided river which are in the 48-meter thick medial part, and the St, Sp and Sh represent deposits of sandy braided river which are in the 240-meter thick lower part; （4） based on the analysis of sedimen- tary log which shows coarsening-upward trend, we deduce that the rate of deposition of alluvial fan was higher than that of subsidence of the basin. The proximal part is superimposed on the distal part due to the progradation of the alluvial fan.