Diverse Polygonal Patterned Grounds in the Northern Eridania Basin, Mars: Possible Origins and Implications

Diverse polygonal patterned grounds are found to occur in the Eridania basin system (a set of connecting irregular-shaped depressions interpreted as a paleolake basin system) located in the martian highland region between Terra Cimmeria and Sirenum. We here use multiple sets of imagery to document diverse polygonal patterned grounds in the fluvio-lacustrine deposits of the northern Eridania basin, and interpret their formation mechanisms. The combination of detailed geomorphological mapping, morphometrical analyses, and investigation of the spatial distribution of polygonal patterned grounds with other geologic features leads us to conclude that (1) desiccation process within the clay-rich materials would primarily contribute to the formation of cracked polygons, while the ridged polygons are best explained by mineral-filled fractures that have been cemented and variably indurated by fluids; (2) the correlation between polygon size and topography is observed in the northern smooth light-toned basement units, which can be best explained by the concentration of salt minerals (such as sulfate) in topographic lows so that the growth of fracturing is inhibited; (3) the large polygonal ridges formed in the knobby light-toned terrains show a spatial distribution and a trend controlled by basin-scale compressional tectonics and influenced by preexisting topography, for example, impact structures; (4) the linear fracture-to-ridge gradation indicates that the polygonal ridges in chlorides might be guided by the subjacent cracks occurring within clay-rich materials; (5) both features (cracks and ridges) in some places may have formed simultaneously and are spatially distinct due to differences in erosional states; and (6) geologic features show a wealth of information of multiple aqueous events with the evaporation of the last liquid water ponding to form the southern playa where chloride salt precipitates. Crater retention age determination for the chloride-bearing basement unit places a lower limit for the cessation of the local aqueous events to similar to 3.29 Ga, indicating that the open-system-style alteration by surface waters on Mars might have continued in the period of the Late Hesperian to Early Amazonian.