Sedimentary deposits are common within Valles Marineris. Most of the larger chasmata contain kilometer-thick light-toned layered deposits composed of sulfates. However, some of the chasmata, like Ius Chasma shown in this HiRISE image, either lack these deposits or have much thinner deposits.
The light-toned deposits in Ius Chasma are observed both along the floor and inner wallrock materials. Some of the light-toned deposits appear to post-date formation of the chasma floor, whereas other deposits appear to lie beneath wallrock materials, indicating they are older. [More at link]