准噶尔乌夏前陆冲断带二叠系层序地层划分及时空演化
Sequence stratigraphic division and spatio-temporal evolution of the Permian strata in the Wuxia foreland thrust zone in the Junggar Basin
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摘要: 造山带地区构造运动复杂、沉积体系多变,其层序地层划分往往被视为禁区。准噶尔盆地西北缘乌夏前陆冲断带早二叠世发育了一套由火山-火山碎屑岩和正常碎屑岩互层的沉积组合,中晚二叠世主要发育了冲积扇相、扇三角洲相和湖泊相沉积,给层序地层学的研究带来很大难题。对前陆冲断带层序地层划分不能套用稳定地区的模式。本文通过地震、钻测井资料识别各类不整合面,并依据火山喷发方式、火山旋回、沉积旋回分析技术,在经典层序地层学基础上按照不同对比原则,进行层序界面的识别和划分,建立了研究区前陆冲断带地区的层序时空演化模式。结果表明:研究区二叠系层序发育经历了强烈俯冲碰撞造山期-饥饿深水阶段、弱冲断夹短暂伸展火山期-复理石阶段、强烈冲断复活期-磨拉石阶段和冲断活动鼎盛期-水下粗粒沉积阶段(PSS4发育期)。Abstract: The Wuxia foreland thrust zone on the northwestern margin of the Junggar Basin is characterized by complicated tectonics, severe stratigraphic deformation and modification, incomplete and variable sedimentary systems, and frequent rising and lowering of sea-levels or lake levels, and has recorded the evolution from foreland basin through intracontinental depression to tectonic uplift since the late Hercynian orogeny. The Early Permian strata in the study area primarily consist of volcanic-volcaniclastic rocks and normal clastic rocks. The alluvial fan facies, fan delta facies and lacustrine facies were accentuated during the Middle and Late Permian. The Jiamuhe Formation is made up of the mixed volcanic rocks, volcaniclastic rocks and clastic rocks, which are assigned to the Smith strata with cyclicity. The regional structural unconformity is believed to be the major factor controlling the development of the Permian sequences and sedimentary characteristics. The Permian strata are classified into four second-order sequences and twelve third-order sequences. The model for the spatio-temporal evolution has been constructed for the Permian strata in the Wuxia foreland thrust zone in the Junggar Basin.