Along-slope bottom currents and down-slope (gravity-driven) turbidity currents coexist in the ocean and interact during their flow processes. The interaction between turbidity currents and bottom currents plays a crucial role in determining the lateral stacking of sediments and the direction of channel migration. Currently, there is ongoing debate regarding the migration direction, with two primary contrasting views: upstream migration versus downstream migration relative to the bottom current. However, due to the challenges in directly observing unidirectionally migrating channels in nature, the sedimentary hydrodynamics and underlying flow mechanisms remain poorly understood. In this study, we employ numerical simulations to systematically analyze the internal flow characteristics and depositional patterns within channels subjected to varying degrees of confinement. Our results demonstrate that variations in channel confinement influence the intensity of the interaction and the nature of the secondary flow, ultimately determining the spatial distribution of sediments. As confinement decreases, the migration pattern of a channel changes from negligible migration to migration in the downstream direction of the bottom current. Subsequently, it changes to migration in the upstream direction of the bottom current. This research provides a novel theoretical perspective for understanding the diametrically opposite migration directions of unidirectionally migrating channels and insights into the turbidity–bottom current interaction processes and the evolutionary mechanisms of deep-sea depositional geomorphology.

The Miocene Sanya, Meishan, and Huangliu formations in the Qiongdongnan Basin (QDNB) record a complete evolutionary history of submarine fan systems, yet a continuous Miocene-scale depositional framework has not been established for the Northern Lingshui Sag. Using 3D seismic data, this study investigates the paleogeomorphological reconstruction, channel system architecture, channel-sink correspondence, and controlling factors of Miocene submarine fans within the Northern Lingshui Sag, QDNB. Paleogeomorphological reconstruction reveals three fundamentally different slope configurations. The Sanya Formation is characterized by a gentle ramp-like slope (1–2°) with high accommodation. The Meishan Formation exhibits a steep structurally partitioned slope (eastern part ~9°, western part 8° decreasing to 2°) with a confined trough in the east. The Huangliu Formation shows a mature moderate slope (3–4°) with reduced structural confinement. Channel system architecture shows fifteen NW-SE oriented channels in the Sanya, six N-S oriented channels in the Meishan, and seven bidirectional channels in the Huangliu. Channel-sink correspondence is strong in the Sanya, localized in the Meishan, and weak in the Huangliu. Fan evolution was driven by three controlling factors: relative sea-level fluctuations, sediment supply and provenance, and paleogeomorphology. Global eustatic falls at 23.0 Ma (T60), 15.5 Ma (T50), and 10.5 Ma (T40) facilitated fan development within lowstand systems tracts. The Ningyuan River supplied sand-rich sediment to the Sanya, the Lingshui River supplied mud-rich sediment to the Meishan, and dual Ningyuan and Lingshui rivers supplied low-flux mud-dominated sediment to the Huangliu. Two major transitions are identified: the Sanya-to-Meishan transition (ca. 15.5 Ma) represents channel reorientation from NW-SE to N-S, reduction from fifteen to six channels, and shift from sand-rich to mud-rich supply; the Meishan-to-Huangliu transition (ca. 10.5 Ma) represents channel reorientation from N-S to bidirectional, increase from six to seven channels, and shift from mud-rich to low-flux mud-dominated supply.