准噶尔盆地南缘上侏罗统-下白垩统地层不整合成因和构造演化意义——齐古断褶带剖面的启示

Origins of the Upper Jurassic-Lower Cretaceous Unconformity and Its Tectonic Significance in the Southern Margin of the Junggar Basin:Insights from Outcrops of the Qigu Fold Belt

为了深化准噶尔盆地南缘新生代前构造演化研究,以准噶尔盆地南缘山前齐古断褶带上侏罗统-下白垩统露头剖面为例,利用野外地质调查、二维地震剖面解释、无人机航拍建模,分析上侏罗统和下白垩统地层之间地层接触关系,结合重矿物不稳定系数和地层厚度分布,得出区域不整合的成因,建立准噶尔盆地南缘山前晚侏罗世-早白垩世构造演化模式。结果表明:准噶尔盆地南缘齐古断褶带上侏罗统喀拉扎组和下白垩统清水河组地层之间存在角度不整合,与中-晚侏罗世欧亚板块南缘一系列的碰撞拼合背景下构造变形引起的剥蚀密切相关。自晚侏罗世进入挤压构造背景以来,天山北缘的构造活动经历了由强到弱的过程,强烈的构造抬升使得喀拉扎组沉积范围明显缩小并整体遭受暴露剥蚀,清水河组超覆在喀拉扎组地层之上形成区域不整合。

In order to profound the research about the pre-Cenozoic tectonic evolution of the southern Junggar Basin.taking outcrop sections of the piedmont Qi ancient fault fold belt at the southern margin of the Junggar Basin during the Jurassic-lower cretaceous as an example,field geological investigation,2D seismic profile interpretation and modeling of unmanned aerial vehicle aerial photography were utilized to analyze the stratigraphic contact relationship between the upper Jurassic and lower Cretaceous beds.Combined with the instability coefficient of heavy minerals and the distribution of strata thickness,the origin of regional unconformity was derived.The late Jurassic-Early Cretaceous tectonic evolution model of the Piedmont in the southern margin of the Junggar Basin was established.The results show that there is an angular unconformity between the upper Jurassic Kalaza Formation and the lower Cretaceous Qingshuihe Formation in the Qigu fault-fold belt on the southern margin of the Junggar Basin,which is closely related to the denudation caused by structural deformation in the background of collision and amalgamation of several blocks in the southern margin of the Eurasian plate.Since the compression tectonic setting during the late Jurassic,the tectonic activity of the northern margin of the Tianshan Mountain has experienced a process from strong to weak.The depositional range of the Kalaza formation is significantly reduced due to exposed erosion by the strong tectonic uplift.The Kalaza formation is overlapped by the Qingshuihe formation to form the regional unconformity.