Genesis and Depositional Environments of Stacked Gravity‐Flow Sandbodies in the Chang 6 Member, Maling–Qiaochuan Area, Ordos Basin, China

ABSTRACT Abundant stacked sand bodies are developed in the Chang 6 Member (the sixth reservoir unit of the Yanchang Formation) within the Maling–Qiaochuan area of the southwestern Ordos Basin. Through integrated analysis of core observations and well‐log interpretations, this study investigates the stacking patterns, spatial distribution characteristics of gravity flow sand bodies and associated depositional environmental changes. The results demonstrate that: (1) Based on the ‘lithology‐sedimentary structure’ classification scheme, seven distinct lithofacies types were identified, including massive sandstone, parallel‐laminated sandstone and normal‐grained sandstone, which were formed through different gravity‐flow depositional processes. (2) These lithofacies assemblages form four principal types of stacked sand bodies with different gravity‐flow origins: multi‐period thick‐layered type (continuous sandy debris‐flow deposits), sand‐thick and mud‐thin type (discontinuous sandy debris‐flow deposits), sandstone–mudstone interbedded type (mixed origin from turbidity currents and sandy debris flows) and sand‐thin and mud‐thick type (primarily late‐stage turbidity‐current deposits, with contributions from the heads of mud‐rich sandy debris flow). (3) The stacked sand bodies exhibit distinct channel features, with the main channel sediments transitioning from multi‐period thick‐layered sand bodies to sand‐thick and mud‐thin type and sandstone–mudstone interbedded type. As the semi‐deep to deep‐lacustrine areas in the Chang 6 3 to Chang 6 1 members shrank, the scale of gravity flows diminished. Key factors contributing to this phenomenon include the weakening of seismic and volcanic activities during the Chang 7 to Chang 6 period as the triggering mechanism and the climatic shift from humid to arid‐semi‐arid conditions caused by the reduced influence of the Carnian Pluvial Event (CPE).