深水块状砂岩碎屑流成因的直接证据:“泥包砾”结构——以鄂尔多斯盆地上三叠统延长组研究为例

“Argillaceous parcel”Structure: A direct evidence of debris flow origin of deep-water massive sandstone of Yanchang Formation,Upper Triassic,the Ordos Basin

水下碎屑流沉积是近年来在深水环境(深海或深湖)中日益受到重视的一种沉积类型,然而目前还没有一个确定水下沉积物的块体搬运过程的公认鉴别标志。通过对鄂尔多斯盆地湖盆中央地区几个露头剖面的地质调查,首次在延长组深水厚层块状砂岩中发现了一种"泥包砾"结构,并分析了其形成与演变过程。研究认为这种"泥包砾"结构主要与三角洲前缘特殊的"碎屑流"成因机理与发育过程有关,其形成过程自始自终表现出含有它的沉积物是作为块体状态(宾汉塑性体)被搬运的,自始自终表现出其在搬运过程中是被介质的强度所支撑的,据此认为"泥包砾"结构是确定延长组深水厚层块状砂岩为碎屑流成因的最有意义的标志性证据,并由此建立了延长组深水砂岩从开始启动到搬运、再到沉积的过程与模式。同时,本文认为"泥包砾"也为深海沉积中块体搬运作用与搬运过程的研究提供了一种可借鉴的关键性判识标志,对于当前全球深水(包括深海与深湖)油气勘探以及目前国际地学界广泛开展的大陆边缘沉积物"从源到汇"过程的研究都有积极意义。

Subaqueous debris flow controlled by mass transport process is a sedimentation type in deep-water( deepmarine or deep-lacustrine) environment increasingly recognized in recent years. However,at present,there are no accepted criteria to identify the mass transport process of subaqueous sediments. Through the geological survey of several outcrop profiles in the center of the Ordos lacustrine basin,a kind of 'argillaceous parcel'structure has been found for the first time in deep-water thick massive sandstone of Yanchang Formation,and its formation and evolution process have been analyzed. What we can conclude is that this sedimentary structure is mainly related to the specific formation mechanism and development process of'debris flow'in delta front. Its formation process shows that the sediments containing it were characterized by transportation of particles en masse( Bingham plastics) and supported by the strength of medium at all times. Accordingly,we are confident that the 'argillaceous parcel'structure is the one of most significant evidence indicating the origin of deep-water thick massive sandstone of Yanchang Formation as debris flow. Consequently,the model of transport process from the start to transport and then to sedimentation of Yanchang Formation deep-water sandstone is established. Moreover,this paper attempts to point out that the'argillaceous parcel'structure is also a key identification marker for identifying the mass transport and its process in deep-marine sedimentation,and that our work is not only significant for the global deep-water( deep-marine and deep-lacustrine)oil & gas exploration but also positive for the'source to sink'research of sediments in the continental margins that is widely performed in the current geoscience field.