抄録
Soft-sediment deformation structures (SSDs) record sediment instability and transient dynamic disturbances, but their formation conditions and tectonic significance remain poorly constrained. We investigate the Upper Triassic Maichuqing–Sanhedong succession in the northeastern Lanping Basin using integrated stratigraphic, sedimentological, lithofacies, and SSD analyses. The succession records a progressive transition from terrigenous siliciclastic to transitional and shallow-marine depositional systems, accompanied by systematic changes in sedimentary conditions. SSDs are strongly stratigraphically selective and spatially heterogeneous, and their stratigraphic relationships and deformation characteristics indicate a predominantly syndepositional to early consolidational origin. Their occurrence reflects sedimentary preconditioning by water saturation, grain-size and density contrasts, rapid deposition, and local slopes, followed by transient disturbances that may have driven susceptible sediments beyond stability thresholds through liquefaction, loading instability, and gravitational deformation. We identify a dual-scale tectonic influence in which long-term Paleo-Tethyan tectonism regulated basin architecture and depositional-system evolution, whereas short-lived syn-depositional disturbances may have triggered SSD formation. We propose a “background regulation–event triggering” framework linking long-term tectonic control of depositional conditions with transient sedimentary responses, providing a process-based interpretation of SSDs as stratigraphically constrained records of multiscale tectonic–depositional coupling.
