Landforms and chronologies in the southern branch of Kasei Valles, MARS

The second-largest valley on Mars is Kasei Valles. This research focuses on the landforms produced by surface processes in the southern branch of Kasei Valles’s midstream. By using cross-cutting relationships, and empirical crater dating of landforms, we constructed a morpho-stratigraphical chronology of the valles. Landforms such as deeply eroded canyons, colluvial fans, landslides, topographic barriers, terraces, and trim lines are typical landforms that have been formed by surface processes.

Our geomorphic mapping reveals that the valles were temporarily obstructed by two colluvial fans and a landslide, creating topographical obstacles to impound fluids (e.g lava, mudflow, water). The toe of the alluvial fans and the landslide were eroded by flights of terraces and trim lines, indicating a temporary, water-like liquid presence in the channel of the valles. The surface texture of the terrace surfaces indicates that the terrace staircases were probably created by a water-like fluid that stagnated and fluctuated for a while before the final evacuation.

The chronology of these important events indicates that colluvial fans were deposited in two temporal clusters. The first colluvial fan generation was formed in the Early Amazonian period (1.74-1.14 Ga), and the second colluvial fan generation was formed in the Late-Middle Amazonian period (307 Ma). The landslide is significantly younger and is estimated to have formed 122 Ma ago. The floor of the valles’s channel is covered by platy-textured material, which was formed 90 Ma ago as lavas or mudflows, which is the youngest studied geomorphologic feature. The age of the landslide and valles’s floor help us to constrain the timing of erosional processes responsible for the flights of terraces and trimlines, which stretch along approximately 60 km from up to downstream. Accordingly, these features should be formed between 122 Ma and 90 Ma. We believe that the genesis of these features (terraces and trimlines) is associated with a Newtonian fluid (such as water) that ponded behind the colluvial fan dams and the climatic conditions that allow this fluid to stagnate over brief periods of time enough to form terraces and trimlines.