Middle Ordovician mass‐transport deposits from western Inner Mongolia, China: Mechanisms and implications for basin evolution
Middle Ordovician mass‐transport deposits from western Inner Mongolia, China: Mechanisms and implications for basin evolution
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DOI：
10.1111/sed.12949
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发表时间：
2021-10
期刊：
影响因子：
3.5
通讯作者：
Wenjie Li;Jitao Chen;Anne J. Hakim;P. Myrow
中科院分区：
文献类型：
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作者：
Wenjie Li;Jitao Chen;Anne J. Hakim;P. Myrow
水下物质输运过程是沉积物输运到深海的机制之一。相对于硅质岩相，碳酸盐物质搬运沉积物的内部结构和沉积过程的了解相对较少，因为它们在岩石记录中相对较少。内蒙古西部（乌海）中上奥陶统斜坡沉积中发育多种碳酸盐物质搬运沉积，包括滑塌、碎屑岩和深河道约束密度流沉积。这些提供了一个难得的机会，说明在露头规模的碳酸盐岩质量输送矿床的侵位历史。滑塌和碎屑岩具有明显的褶皱、杂乱层和叠瓦状层，反映了流变学和斜坡位置的差异。单个滑塌岩片显示起伏纹层、倾斜和平卧褶皱、高度变形褶皱和从趾部向上倾斜的混乱结构之间的渐变。碎屑岩常与滑塌沉积互层，而在滑塌岩席趾部的中下部，靠近端壁处则有叠瓦状层。在研究区域，Kelimoli组的薄层灰岩和滑塌沉积物被Wulalike组的细粒、硅质岩为主的斜坡沉积物覆盖。在乌海东南部的主补给河道中沉积了乌拉里克组的厚角砾岩，但在西北偏西方向，角砾岩沉积在分流河道中，可能表现为独特的低坡度冲沟模式。在后一地点，角砾岩仅沉积在密度驱动流作用下西北-西北倾斜陡坡上的河道内。本文记录的物质搬运沉积物记录了被动前陆盆地构造转换，以及相关的台地下沉和斜坡变陡。斜坡相模型的构建，以证明在盆地演化过程中的质量输送沉积物的空间和时间变化，因此，它提供了一个模板，古斜坡的沉积物经历了被动到主动的构造转换的解释。
Subaqueous mass‐transport processes are one of the mechanisms for transport of sediment into the deep sea. Internal structures and depositional processes of carbonate mass‐transport deposits are relatively poorly understood relative to siliciclastic facies due to their comparative paucity in the rock record. A variety of carbonate mass‐transport deposits, including slumps, debrites and deep‐channel‐confined density flow deposits, occur in Middle–Upper Ordovician slope deposits in western Inner Mongolia (Wuhai), China. These provide a rare opportunity to illustrate the emplacement history of carbonate mass‐transport deposits at the outcrop scale. The slumps and debrites host remarkable folds, chaotic beds and imbricated beds that reflect differences in both rheology and position on the slope. Individual slump sheets show gradations between undulating laminae, inclined and recumbent folds, highly deformed folds, and chaotic textures upslope from the toe region. Debrites are commonly interbedded with slump deposits, whereas imbricated beds are present in the middle and lower parts of the toes of slump sheets near the terminal wall. In the study area, thin‐bedded limestone with slump deposits of the Kelimoli Formation are overlain by fine‐grained, siliciclastic‐dominated, slope deposits of the Wulalike Formation. A thick breccia of the Wulalike Formation was deposited in a main feeder channel in south‐east Wuhai, but to the west‐north‐west the breccia was deposited in distributary channels possibly represented as a unique lower‐slope pattern of gullies. At the latter locality, the breccia was deposited solely within the channels on a steep west‐north‐west dipping slope under density‐driven flows. The mass‐transport deposits documented herein records passive to foreland basin tectonic transitions, and associated platform foundering and steepening of the slope. A slope facies model was constructed to demonstrate the spatial and temporal variations of mass‐transport deposits during basin evolution, and as such it provides a template for the interpretation of the deposits of ancient slopes that underwent passive to active tectonic transitions.