Fig. 2: The distribution, lithological units, and chronology of lacustrine sediments, along with the longitudinal profile of the valley.

a Lake deposits overlaid onto Google imagery, showing the spatial distribution of the outcrops. b Elevation of the ancient channel and field photos of the outcrops. We can observe from the reach between outcrops 2 and 3 that the underlying bedrock has been uplifted above the general level of the ephemeral channel of the Duanshankou. To determine the longitudinal profile of the palaeochannel, we surveyed the elevation of the modern river valley, using differential GPS (Huace T12 PRO), with an average point spacing of 0.2 m (Fig. 2b). In addition, we performed single-point measurements at locations where lacustrine deposits interface with the underlying strata (gravel layers or bedrock) exposed within the valley. These data were used to correct the modern riverbed elevation and accurately restore the palaeochannel morphology. All data were processed and visualized using ArcGIS software. The longitudinal profile of the palaeochannel reveals channel deformation affecting the river. c Stratigraphic panel showing lithostratigraphy, sedimentology, and OSL ages at outcrops along the modern Duanshankou River. The imagery in a is sourced from Google Maps (Image ©2025 Google), with data from Maxar Technologies, Airbus, and CNES/Airbus.