The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) discovered a particularly complicated area of sedimentation on Mars. It occurs along the southern margin of Melas Chasma, one of the large troughs of the Valles Marineris system, and reveals part of the geologic history of ancient Mars.

Sedimentary rocks are created when weathering breaks down older rock, and wind and water transport the rock fragments to a location where they are deposited and subsequently lithified, or turned back into rock, by cementation and compaction.

According to Malin Space Science Systems (MSSS), builders and operators of the MOC, these images show a portion of a topographic depression eroded into layered rocks. Erosion has revealed layers of different ages, the oldest at the bottom of the depression. Within this depression are two sets of alluvial, or water-lain, sedimentary rock units that retain their original shape, indicating how the sediments were deposited before the material became rock. In these cases, the processes created fans of debris with finger-like protrusions at the ends and sides of the fans. Also preserved are the channels through which water and sediment flowed. In the two figures, the pictures are identical except that, on the left, the fans have been colored to indicate their location. Long after these fans were formed, they were buried and subsequently uncovered by more recent erosion.

Figures A and B are map-projected mosaics, taken in 2003 and 2004, respectively, during the second MGS mission extension, the third Mars year that MGS was in its nearly-circular, nearly-polar mapping orbit.

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--Malin Space Science Systems (MSSS) and SPACE.com Staff

Credit: NASA/JPL/Malin Space Science Systems