Analysis of sedimentary types, patterns, and controlling factors of deep-water gravity flow in terrestrial depression lake basins: Takeing Chang 7 member of Yanchang Formation of Ordos Basin as an example

The deep-water sedimentary system of Chang 7 in the Ordos Basin is a typical representative of deep-water gravity flow in large depression lake basins. Exploring the types, characteristics, fluid properties, and sedimentary evolution process of deepwater gravity flow sedimentation in Chang 7 based on centimeter level core descriptions, logging, and thin section data from multiple core wells. There are four types of deep-water sedimentation: deep lake mud shale sedimentation, landslide sedimentation, sandy debris flow sedimentation, and turbidity current sedimentation. The delta front sand body on the profile undergoes collapse under external force triggering conditions, transforming into sandpaper debris flow and ultimately evolving into turbidity current. On the plane, a large area of sandy debris flow tongue shaped bodies are developed at the end of the delta front slope break zone, and turbidite deposits are distributed in a fan-shaped pattern. The unique tectonic background and climatic conditions of the Late Triassic in the Ordos Basin, as well as strong orogenic activity, formed a gravity flow sedimentary model unique to this type of large depression lake basin. The sandy debris flow and turbid flow sand bodies are the first and second types of sand bodies of Chang 7 shale oil, respectively, and have currently formed economies of scale.