A revised chronological formation of fretted terrains on Mars

Fretted terrains are among the most striking geomorphological features on Mars. Predominantly developed in a 500-km-wide zone located along the dichotomy boundary especially between 270°W and 360°W in regions such as Deuteronilus Mensae, these landscapes are characterized by parallel ridges, troughs, and mesas separated by broad valleys. Understanding their formation provides critic insights into the geological and climatic evolution of Mars. Here we suggest that the development of fretted terrains occurred in several major stages, beginning with tectonic activity in relation with the formation of Tharsis, contemporaneous with fluvial erosion, and ending with glacial processes that further modified the landscape.

During the Late Noachian to Early Hesperian periods, Mars experienced significant crustal stress associated with the formation of Tharsis and the resulting true polar wander, leading to regional uplift along the fretted terrains. This stress generated extensional fractures and fault systems with the formation of kilometer scale U-shaped valleys. The resulting landscape consisted of plateaus and isolated mesas delineated by steep scarps.

The Mars’s climate is thought to have undergone a period of relative warm and wetter regime during the Hesperian period. During this time, heavy rainfall or snowmelt events likely led to widespread fluvial erosion. Water flowed through the pre-existing tectonic valleys, widening them into large troughs or “fretted” corridors. Fluvial processes removed material from the highlands and transported sediments northward, to the low-lying basins of the northern plains with the formation of a large sedimentary accumulation north of the fretted terrains.

The final phase in the evolution of fretted terrains was dominated by recent glacial activity. As Mars cooled during the Late Hesperian to Amazonian periods, the climate became colder and drier, leading to the accumulation of ice within the valleys.
Evidence for this glacial phase mostly includes lineated valley fills. The glaciers likely originated from snow accumulation on the plateau surfaces, which then flowed down into the valley postdating the fluvial episod.