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

Key words: 
• &ldquo /
• argillaceous parcel&rdquo /
•  /
• mass transport /
• sandy debris flow /
• Yanchang Formation /
• Ordos Basin

Abstract: Subaqueous debris flow controlled by mass transport process is a sedimentation type in deep-water (deep-marine 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.