Geological Responses to the Coupling Effect Between Mass and Slope in the Meandering‐Braided Transition System

ABSTRACT This study examines the role of the coupling effect between mass and slope, defined as the coordinated variation in particle grain size and topographic slope, in explaining the transition from meandering to braided fluvial systems and elucidates the associated three‐dimensional geological responses. In the Lower Triassic of the southern Junggar Basin, a well‐developed meandering‐braided transition system is documented, with well‐exposed sedimentary sections offering insight into the transformation process. Palaeoslope estimation and particle grain analysis confirm the presence of the coupling effect between mass and slope in the study area. This effect is characterised by a general positive correlation between topographic slope and particle grain size and may have contributed to the formation of the meandering‐braided fluvial system. Palaeoslope estimation was conducted using Long's (2022) empirically validated formulas, with cross‐beds ( H x) and median grain size ( Di 50) as key input parameters. The vertical sedimentary succession, section stacking patterns and quantitative characterisation of architectural elements from meandering to braided fluvial systems collectively record geological responses during the fluvial pattern transition process.