摘要：

山西永济中条山地区长城系沉积了一套以碎屑岩为主的海相地层,是鄂尔多斯地区最早的沉积地层,完整记录了长城纪的裂陷活动。自下而上发育了白草坪组、北大尖组、崔庄组和洛峪口组。其中,白草坪组与北大尖组被认为以石英砂岩为主,崔庄组为页岩,洛峪口组为白云岩。本次研究在中条山陶家窑剖面中发现大量混合沉积,类型多样,在以往关于鄂尔多斯地区长城系的研究中鲜有报道,对于混合沉积成因与沉积模式缺乏系统认识。通过宏观的野外沉积物结构和沉积构造分析,结合微观的室内显微镜观察,以明确中条山地区长城系混合沉积特征与类型,进而揭示混合沉积的成因与模式。研究表明,白草坪组为具有块状构造的相混合沉积; 北大尖组发育原地混合、相混合与间断混合沉积,呈中—薄层夹于发育交错层理的石英砂岩中; 崔庄组发育少量相混合沉积; 洛峪口组主要发育母源混合沉积。混合沉积的过程受裂谷作用控制: 早期受裂谷活动影响,为陡坡地貌,缺少原地混合条件,以相混合为主; 北大尖组沉积时期,裂谷作用减弱,形成缓坡地貌,发育了相混合、原地混合以及间断混合。洛峪口组沉积时期,裂陷作用结束,海平面大幅下降,早期沉积的碳酸盐岩出露被剥蚀,以内碎屑的形式搬运至盆地内部与石英共同沉积形成母源混合。整体上,混合沉积均出现在各组顶部的海平面开始加速上升时期,因此海平面上升在一定程度上是决定混合沉积的基础条件。

关键词: 混合沉积, 混积类型, 沉积模式, 长城系, 中条山, 山西省

Abstract:

A set of marine strata dominated by clastic rocks was deposited during the Changchengian period in the Zhongtiao Mountain region of Yongji,Shanxi. These strata are the earliest sedimentary strata in the Ordos region,recording a complete history of the rifting activities during the Changchengian period. The strata contain four lithostratigraphic units including,from bottom to top,the Baicaoping,Beidajian,Cuizhuang,and Luoyukou Formations. Among them,the Baicaoping and Beidajian Formations are dominated by quartzose sandstones,the Cuizhuang Formation by shale,and the Luoyukou Formation by dolomite. In this study,various mixed sedimentary deposits were discovered in the Taojiayao section of the Zhongtiao Mountains. This study combines field sedimentary structures with microscopic observations to clarify the characteristics and types of mixed sedimentary deposits and further reveals their origins and patterns. The result shows that the Baicaoping Formation is a mixed-facies deposit with massive structures;the Beidajian Formation contains in-place mixing,phase mixing,and intermittent mixing deposits,presented as medium-to-thin layers interspersed in cross-bedded quartzose sandstone;the Cuizhuang Formation develops a small amount of mixed-facies deposition;the Luoyukou Formation mainly contains source-mixed deposits. The mixed sedimentary processes were controlled by rifting: in the early stage with intense rifting,the steep slope landform was dominated by mixed facies;during the Beidajian period with weakened rifting,a gentle slope formed,leading to the development of mixed-facies,and in-place and intermittent mixing deposits;during the Luoyukou depositional period when rifting ended and sea-level dropped significantly,the carbonate rocks deposited earlier were exposed and eroded,and transported into the basin interior as internal debris forming source-mixed deposits. Overall,mixed deposits appeared at the top of each formation during the period when the sea-level began to accelerate,suggesting that sea-level rise was a fundamental condition for determining mixed deposition to a certain extent.

Key words: mixed sedimentation, types of mixed sedimentary deposits, patterns of mixed sedimentary deposits, Changchengian, Zhongtiao Mountain, Shanxi Province

中图分类号: 

• P588.2