Preprints
https://doi.org/10.5194/egusphere-2023-2651
https://doi.org/10.5194/egusphere-2023-2651
19 Jan 2024
 | 19 Jan 2024
Status: this preprint is open for discussion.

Drainage rearrangement in an intra-continental mountain belt: A case study from the central South Tian Shan, Kyrgyzstan

Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, and Apolline Mariotti

Abstract. Fluvial drainage patterns in orogenic belts reflect the interaction between tectonics, climate, and lithology. The central South Tian Shan displays a complex fluvial drainage pattern that shifts from longitudinal (flowing parallel to mountain ranges) in the west to transverse (flowing across ranges) in the east. Whether such drainage patterns reflect underlying patterns of tectonic deformation, lithology, climatic changes, or the influence of surface processes within a drainage basin is often unclear. We focus here on the anomalously large Saryjaz catchment of SE Kyrgyzstan, which marks the transition between longitudinal and transverse drainage. We analyse topographic and fluvial metrics including slope, river steepness (ksn) and the integral proxy χ along the river profile, and map the spatial distribution and characteristics of knickpoints to discern the possible controls on the observed drainage pattern. We discriminate between knickpoints of different origin: tectonic, lithologic, glacial, and those linked to transient waves of incision. We find a series of transient knickpoints in tributaries downstream of a sharp 180ᵒ bend in the main stem of the Saryjaz River, which also marks a striking increase in channel steepness. Both observations indicate accelerated incision along this lower reach of the catchment. Knickpoint elevations decrease downstream, whereas incision depth, χ values of knickpoints (measured from the tributary junctions) and ksn values and ratios are constant among tributaries. These results suggest that incision is driven “top-down” by a large-magnitude river-capture event rather than “bottom-up” by base-level fall. We estimate an erodibility parameter from 10Be derived catchment-average denudation rates and use this to estimate the celerity of knickpoints. We find that the knickpoints started retreating at a similar time, between ca. 1.5 and 4.4 Myr ago. Considering the river patterns and the timing constraints, we suggest that this capture event was likely driven by the overfill of Neogene intermontane basins, potentially affected by both tectonic and climate factors.

Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, and Apolline Mariotti

Status: open (until 05 Mar 2024)

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Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, and Apolline Mariotti
Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, and Apolline Mariotti

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Short summary
The central South Tian Shan displays a complex river pattern spatially. We choose the transition zone in between and analyse topographic and fluvial metrics along the river profile. Considering the river patterns and the timing constraints, we suggest that the river patterns were triggered by a big capture event, potentially affected by both tectonic and climate factors. This conclusion underlines the importance of local contingent factors in driving drainage development.