Segment boundary controls on unconfined turbidity currents: Numerical modelling of collinear segmented folds

Turbidity current pathways and depositional patterns in tectonically active deep-water basins are strongly influenced by evolving fold-related topography, yet the hydraulic mechanisms governing sediment routing across segmented fold systems remain poorly constrained. Here, we integrate geodynamic modelling of fault-related fold growth with computational fluid dynamics (CFD) simulations of unconfined, natural-scale turbidity currents to examine how progressive linkage of collinear folds controls flow behaviour and sediment dispersal. The simulations show that flow reflection at fold backlimbs is dominated by dense basal reverse underflow, which accounts for more than 98 % of upstream sediment transport during reflection. This process governs the development of upstream hydraulic jumps, sustains subcritical flow regimes, and promotes the accumulation of thick, relatively coarse-grained deposits along fold backlimb bases. The response of turbidity currents is further shown to be highly sensitive to the relief of fold segment boundaries, quantified by the linkage ratio. During early linkage stages, broad, low-relief segment boundaries focus axial flow and permit efficient sediment bypass. With progressive linkage, increasing boundary relief enhances flow reflection and suppresses direct axial bypass during late linkage stages. As fold linkage advances, sediment pathways are re-routed from axial bypass across segment boundaries to lateral diversion around outer fold tips. This transition does not result in complete basin isolation but instead produces a dynamic balance between sediment retention and bypass. Even in tightly linked fold systems, individual turbidity current events typically trap no more than ~40 % of suspended sediment, with the remainder spilling into downstream minibasins through alternative pathways. These results demonstrate that classical ‘fill-and-spill’ models capture only part of sediment dispersal behaviour in growing fold systems. Incorporating three-dimensional flow reorganization and evolving structural connectivity provides a more realistic framework for interpreting sediment routing and stratigraphic architecture in syn-tectonic deep-water basins.