One of the unresolved questions by scientists studying the Valles Marineris canyon system concerns the relative ages of light-toned and dark-toned layered deposits inside the canyon troughs.

Some scientists argue that the light-toned layered deposits are relatively young units that were deposited on top of older dark-toned layered deposits after formation of the troughs. Others favor the idea that the light-toned layered deposits are exhumed from the wallrock by trough formation and were formed concurrently with the dark-toned deposits.

The dark-toned layered deposits define the wallrock of Valles Marineris system and have been interpreted primarily as volcanic lavas, sedimentary rocks, and/or layered intrusive rocks. The light-toned layered deposits could be volcanic ash, aeolian deposits, and/or sedimentary rocks possibly deposited in water.

By examining locations where light- and dark-toned layered deposits share a geologic contact, such as this image in East Candor Chasma, scientists hope to determine the relative ages of the two units. Near the bottom of the image, dark-toned layered deposits are exposed on spurs with dark debris aprons along the steeper canyon walls. The light-toned layered deposits are seen to the north along the trough floor.

Written by: Cathy Weitz   (11 July 2007)

This is a stereo pair with PSP_005267_1715 .

More info and image formats at http://hirise.lpl.arizona.edu/PSP_004278_1715

Image: NASA/JPL/University of Arizona