A study of polygonal landforms in the western Qaidam Basin and implications for polygonal landforms on Mars

Keywords: Polygon, Qaidam Basin, Subsurface fluid, Halite crust, Gypsum raised rim, Mars

 

Abstract:

 

Polygonal landforms ranging in size from a few meters to several hundred meters are present in ancient salt playas on Earth and Mars (Anglés and Li, 2017). The formation of these landforms may provide information about the paleoclimate of Mars. The Qaidam Basin is one of the highest, largest, and driest deserts on Earth, located in a dry, cold, and high ultraviolet environment similar to the surface of Mars (Xiao et al., 2017). The historically hyperarid climate of the Qaidam Basin has allowed the development of extensive polygonal landforms with diverse geometric and genetic types. Here we report a terrain characterized by polygons with raised rims, ranging in size from approximately 60 to 120 meters, and exhibiting spatial variation in mineral composition and geometry from the Dalangtan area of the western Qaidam Basin on the Tibetan Plateau.

 

An unmanned aerial vehicle (UAV) was used to capture high-resolution aerial imagery and generate a high-resolution digital elevation model (DEM) through photogrammetric software (Li et al., 2022). Spatially, the polygons in the northeastern part of the study area have complete rims, while the polygons in the southwest have incomplete rims (Fig .1). Surface and subsurface samples were collected at 6-meter intervals from the center to the rim of the polygons and analyzed for mineral composition and content by X-ray diffraction (chung et al., 1974). These polygons consist of a halite crust in the subsurface and raised rims formed mainly of gypsum. In some areas, the polygonal rims are broadened and form boundary belts that are up to ~30 m wide and about 1.2 m high.

 

Through spatial and mineral analysis, we propose a formation mechanism for polygonal landforms: the formation of the halite crust in the subsurface re-directs upward migration of evaporitic pore fluids that accumulate gypsum deposits to form the wide polygonal boundary belts (Lasser et al., 2023; Fig. 2). We suggest that the similarly sized polygons with raised rims on Mars have similar lateral and vertical structures caused successively by the strong evaporation of lacustrine brines and subsurface pore fluids (Zhu et al., 2023).

Figure 1. Digital elevation model (DEM) of the study area generated by an unmanned aerial vehicle survey.

Figure 2. Schematic representations of the formation of the raised rims/boundary belts of the pan-like polygons in the Qaidam Basin. The early stage is characterized by the drying of lacustrine (left column). Continued evaporation causes the surface to dry out and form polygonal cracks. In the middle stage, the halite crust begins to form and diverts the evaporative fluids, and gypsum begins to accumulate at the rim (middle column). In the development stage, the halite crust thickens, and more gypsum is deposited to widen the polygonal rims into wide belts (right column).

 

References

 

Anglés, A., Li, Y. (2017). The western Qaidam Basin as a potential Martian environmental analogue: An overview[J]. Journal of Geophysical Research: Planets, 122(5), 856-888.

 

Xiao, L., Wang, J., Dang, Y., Cheng, Z., Huang, T., Zhao, J., Xu, Y., Huang, J., Xiao, Z., Komatsu, G. (2017). A new terrestrial analogue site for Mars research: the Qaidam Basin, Tibetan Plateau (NW China)[J]. Earth-Science Reviews, 164, 84-101.

 

Dang, Y., Xiao, L., Xu, Y., Zhang, F., Huang, J., Wang, J., Zhao, J., Komatsu, G., Yue, Z. (2018). The polygonal surface structures in the Dalangtan Playa, Qaidam Basin, NW China: controlling factors for their formation and implications for analogous Martian landforms[J]. Journal of Geophysical Research: Planets, 123(7), 1910-1933.

 

Li, Z., Wu, B., Liu, W. C., Chen, Z. (2022). Integrated photogrammetric and photoclinometric processing of multiple HRSC images for pixelwise 3-D mapping on Mars[J]. In IEEE Transactions on Geoscience and Remote Sensing, 60, 1-13.

 

Chung, F. H. (1974). Quantitative interpretation of X-ray diffraction patterns of mixtures. II. Adiabatic principle of X-ray diffraction analysis of mixtures[J]. Journal of Applied Crystallography, 7(6), 526-531.

 

Lasser, J., Nield, J. M., Ernst, M., Karius, V., Wiggs, G. F., Threadgold, M. R., Beaume, C., Goehring, L. (2023). Salt polygons and porous media convection. Physical Review X, 13(1), 011025.Salt polygons and porous media convection[J]. Physical Review X, 13(1), 011025.

 

Zhu, J., Wu, B., Zhao, T., Li, Y. (2023). Polygons with halite-crusted floors and gypsum-raised rims in western Qaidam Basin and implications for polygonal landforms on Mars. Geomorphology, 443, 108934.