The Polygonal Surface Structures in the Dalangtan Playa, Qaidam Basin, NW China: Controlling Factors for Their Formation and Implications for Analogous Martian Landforms

摘要

Abundant polygonal surface structure (PSS) landforms within the Qaidam Basin, Tibetan Plateau, northwestern China, are considered to be excellent analogues for the PSSs on Mars. In this study, we have carried out fieldwork in the Dalangtan Playa, a large dried salt lake in the northwestern Qaidam Basin, complemented with laboratory analyses of collected samples. Our study shows that (1) the playa PSSs can be divided into three groups: small (<10 m), medium (10-100 m), and large (>100 m) according to their sizes; (2) the samples collected from the PSSs are dominated by halite (mostly >50 wt %), followed by feldspar (mostly ~20 wt %), quartz, and minor clays; (3) illite- and chlorite-dominated clay minerals are detected in nearly all medium- to large-sized PSS regions; the average halite content of small-sized PSSs is higher than that of larger PSSs; (4) most small-sized PSSs are distributed on the flat playa floors, while larger PSSs tend to occur at the edge of the Dalangtan Playa with higher elevations. The topography within the Dalangtan Playa controls different mineralogical precipitation primarily due to evaporation processes. Thus, correlations of the size-dependent PSS occurrences and elevations seem to indicate that the PSS formation is strongly influenced by the mineralogy. The geomorphological similarity of these PSSs and their counterparts on Mars indicates that the Martian PSSs likely formed as a result of environmental change from wet to dryer condition, and it also suggests that there are similar controlling factors responsible for the PSS formation onMars.