Abstract DGP2026-56

Polygonal patterned ground is a common phenomenon on Earth and Mars; however, unlike their extensively studied periglacial counterparts, polygons in hyper-arid settings remain poorly constrained despite their potential as analogues for polygonal Martian terrains. The Atacama Desert, one of the driest places on Earth, provides an ideal environment to investigate polygon formation under extreme aridity, low erosion rates, salt enrichment, and minimal biological activity. In this study, we excavated a two-meter deep and five-meter-long trench through dust-covered polygonal ground in the Yungay Valley, located within the hyper-arid core of the Atacama Desert. More than 80 sediment samples were systematically collected, primarily from a 190 × 190 cm section of one trench wall encompassing a polygon center and its respective wedges, with additional samples from other parts of the trench and surface soils. We applied grain size analysis, powder XRD, micro-XRF, and microprobe analysis to characterize the soil mineralogy and salt distribution.

Results indicate that the polygonal network is hosted in alluvial-fan deposits composed of sand-sized clastic sediment strongly cemented by sulfates and chlorides, notably glauberite, thenardite, blödite, and halite, with minor gypsum and anhydrite. Polygon-wedge cracks are assumed to be initiated by thermal contraction driven by strong temperature fluctuations and by sulfate dehydration processes. Over time, cyclic cracking and aeolian infill of loose sediment promote wedge growth. Episodic fog and rare rainfall could redistribute salts within the soil column according to solubility, thereby altering geochemical profiles.

We identified dust-covered polygons beneath the surface, which suggest that polygon networks are more widespread than visible at first glance, a finding with direct relevance for interpreting similar features on Mars. Complementary 2D and 3D ground-penetrating radar (GPR) surveys on the same polygonal field revealed distinct shallow polygonal structures and adjacent sand wedges, demonstrating that GPR can map these subsurface networks where sand and dust mask the surface and drone-based surface mapping becomes unreliable. GPR imaging displayed the underground structure of the sand wedges and surrounding material down to ~3 meters depth and provided hints about the electromagnetic properties of the deposits, which relate to the water content and salinity. The geochemistry of these buried polygons differs from previously studied polygons within the Yungay Valley, which emphasizes the pronounced heterogeneity of polygon networks even over a few hundred meters and raises the question of how a variety of salt assemblages influence polygon formation. Overall, the polygenetic formation of polygonal ground in the Atacama Desert provides an analogue for Martian polygonal ground, especially in hyper-arid sulfate- and chloride-bearing terrains.