Analysis of two sections of Shalbatana Vallis' tributary channels

Two possible scenarios are proposed to explain the formation of these two classes of reaches: (1) They may have formed under different climatic conditions on Mars, and show examples for surface forming forces that changed during the planetary evolution. Such different valley sections may point to differences both in lithology and differences in the Martian surface conditions if they formed at different periods. (2) The other possibility is that they formed roughly during the same period, and the two different sections represent differences only in lithology and erodibility. The incut of the upper reach happened in a harder rock unit, forming a nearly horizontal longitudinal profile, and was not deep enough to reach the deeper, more erodible rock level. At the lower reach a different type of erosion took place because of different lithology, and formed the deeper, steeper lower reaches there.