内蒙古西部北山-银额地区石炭纪-二叠纪层序地层与沉积演化

内蒙古西部北山-银额地区位于华北板块、塔里木板块和哈萨克斯坦板块的交汇带,构造背景复杂,一直是构造研究的热点地区。虽然研究区发育数千米以碎屑岩+火山岩+碳酸盐岩为特征的石炭系-二叠系,但层序地层与沉积演化研究十分薄弱,一定程度上制约了对构造背景的认识。本文通过石炭纪-二叠纪区域地层对比与层序地层研究,分别建立了北山和银额2个地区石炭纪-二叠纪层序地层格架,明确了不同构造单元石炭纪-二叠纪层序地层具有良好的对比关系,为统一构造环境沉积的地质体。通过沉积演化研究,明确了研究区石炭纪-二叠纪具有"两坳一隆"的构造格架,并控制着沉积相的展布,早石炭世晚期北山地区南部接受沉积,之后逐渐伸展,晚石炭世晚期-早二叠世早期盆地沉积范围最大,盆地演化达到鼎盛。早二叠世晚期盆地开始萎缩,晚二叠世海水基本退出研究区,仅银额东北部接受了海相沉积。总之,层序地层及沉积演化研究指示研究区石炭纪-二叠纪为相同构造环境下形成的统一的陆内(板内)裂谷盆地。

The Carboniferous-Permian sequence stratigraphy and sedimentary evolution of Beishan-Yin'e region, western Inner Mongolia

The Beishan-Yin''e region in western Inner Mongolia is located in the convergence area of the North China Plate, Tarim Plate and Kazakhstan Plate. The complexity of tectonic settings makes the region a frontier field. The Carboniferous-Permian lithological association comprised by clastic rocks, volcanic rocks and carbonate rocks are well developed in study area, specifically, with thousands of meters in terms of thickness, however, the analyses of sequence stratigraphy and sedimentary evolution still remain scarce, leading to misunderstanding of its geological settings. Based on the analyses of the Carboniferous-Permian regional stratigraphic correlation as well as sequence stratigraphic, Carboniferous-Permian stratigraphic frames in both Beishan and Yin''e areas were well constructed, respectively, which indicates that Carboniferous-Permian stratigraphic sequence between different tectonic units can be well correlated, probably as the geological bodies deposited in a unified tectonic environment. Based on the analysis of the sedimentary evolution, a tectonic frame of "two depressions with one uplift" of Carboniferous-Permian layers in study area has been clarified, which controlled the distribution of sedimentary facies. In late Early-Carboniferous, the southern part of the Beishan area started depositing, then gradually stretching. The sedimentary range became the largest during late Late-Carboniferous to early Early-Permian, making the extent of basin evolution greatest. From the age of late Early-Permian, the basin started shrinking. This situation lasted until Late-Permian, which led to the marine regression from the study area, only with marine sediments deposited in northeastern part of Yin''e area. In short, the research in sequence stratigraphy and sedimentary evolution indicates that the study area in Carboniferous-Permian was a united intracontinental (intraplate) rift basin under a unified tectonic environment.