Bidirectional clinoform growth: architecture, process and mechanism: Insights from the Triassic Yanchang Formation, Ordos Basin, China

Clinothems hold significant geological implications for understanding lacustrine basin filling, sediment-tectonic coupling relationships, and hydrocarbon exploration. Current clinothem research predominantly focuses on sedimentary evolution of single-provenance systems, mostly limited to marine basins and continental rift basins, with insufficient attention paid to depression-type lacustrine basins, particularly regarding the growth processes and controlling factors of clinothems under multi-provenance systems. Based on newly obtained 3D seismic data, well-developed bidirectional clinothems are identified in the Triassic Yanchang Formation of the Mesozoic Ordos Basin, which is well-known as a typical depression-type lacustrine basin. The results indicate that the C7–C1 members of the Middle–Upper Triassic Yanchang Formation can be divided into six clinothem stages (F1–F6), with clinothem stacking patterns evolving from early progradation to late aggradation. Although the lacustrine basin has developed oblique clinothems with a low overall slope angle (0.43°–1.06°) and low-angle ascending trajectories (0.09°–0.4°), key differences exist: the southwestern part was strongly progradation-dominated, whereas the northeastern part exhibited pronounced aggradation. The relationship between clinoform growth and controlling mechanisms varies spatially. In the southwest, uplift of the southern Qinling orogen initially created high accommodation but limited sediment supply (F1), followed by a phase of increased sediment delivery and progradation (F2–F4), and finally transitioned to aggradation as accommodation and sediment flux neared equilibrium (F5–F6). Conversely, the northeastern sector, more distal and tectonically stable, evolved from early aggradational to late progradational and again aggradational stacking as sediment supply waned. This study provides new insights into how multi-provenance sediment supply and differential tectonic subsidence control bidirectional clinothem growth in lacustrine basins, with implications for predicting reservoir distribution and stratigraphic architecture in similar continental settings. • The Mesozoic Ordos Basin was a typical dual-provenance continental depression lacustrine basin. • The chang7 to chang1 members of the Yanchang Formation is divided into six clinothem stages (F1∼F6). • The clinothem stacking pattern transitioned from early progradation to late aggradation. • The clinoform is dominated by oblique and sigmoidal geometries, with low-angle ascending trajectories. • For depression lacustrine basins, tectonic movements and provenance supply are the main factors affecting clinothem development.