The relationships between tectonics, climate and sedimentation are important for understanding landscape evolution. In order to elucidate these relationships, we conducted a detailed survey of the thickness of terrace deposits and the altitude of terrace surfaces along the Liyuan River valley, in the Northeast (NE) Tibetan Plateau. We have dated the formation ages of terraces T3 and T4 to 42 ± 3.2 and 93.7 ± 7.5 ka, respectively, using optically stimulated luminescence (OSL) method. By compiling the deposit thickness of terraces, palaeoclimate records and local tectonism, we found that variations in precipitation account for the temporal differences in thickness/ rates of sediment deposition in terraces T4 and T3. However, the spatial distribution of terrace deposit thickness was determined by tectonism, including faulting and folding, which changed the local base level. In order to maintain a foreland-warddipping gradient, the Liyuan River adjusts its sedimentary processes via spatially differentiated aggradation.

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The subsurface fault geometry is the base for understanding a process of crust deformation and mountain building. Based on kinematic models for fault-related folds, a geomorphic method is recently applied to estimate the subsurface fault geometry, while the validation on its reliability is lacking. In this study, we surveyed a suit of river terrace surfaces across an active fold at the north front of the Qilian Shan. According to the deformation geometry of the terraces, the fold deformation is interpreted by a listric fault fold model, and based on this kinematic model, the fault geometry underlying the fold is estimated. In comparison between the estimated fault geometry and a seismic reflection profile, we found that the decollement depth and the back thrust are highly consistent with each other. Although some small fault bends or internal shearing cannot be estimated solely by the terrace deformation, the overall fault geometry is successfully revealed by the terrace deformation. Using this fault geometry and the terrace dating results, the region deformation kinematics are re-evaluated, which suggest that the dip slip (in a rate of 1.8 ± 0.4 mm/a) along the decollement is mainly accommodated by two structures, one is the blind-back-thrust fault within the piggy basin in a dip-slip rate of 0.9 ± 0.3 mm/a and another is the thrust and fold at the west portion of the Yumu Shan range.