



Mars Global Surveyor
Mars Orbiter Camera

Sketches Illustrating Processes that Might have Formed Layered Units,
Massive Units, and Thin Mesa Units in Martian Terrain

MGS MOC Release No. MOC2-265P, 4 December 2000


(1) Formation of Layered Units:


(2) Formation of Massive Units


These simplified sketches portray cross-sections through the upper few kilometers (upper few miles) of the martian crust and illustrate the key processes that might have contributed to the formation of layered and massive sedimentary rock units on Mars. Two basic processes are portrayed:
The chief source for sediment in both cases may be a combination of materials produced by explosive volcanism, meteorite impact, and weathering and erosion. Thin layers of regular thickness, as seen in western Candor Chasma, seem most likely to have formed underwater in lakes or perhaps shallow seas, most of them occupying craters. In the "Air Fall" case, a mechanism to create thin layers of regular thickness and properties is needed that would mimic the type of deposition that occurs in bodies of water. In this scenario, the atmosphere's pressure varies on a regular basis from something that is hundreds of times thicker than it is at present, to something that is perhaps only tens of times (or less) thicker than it is today. As the atmospheric pressure goes up, it could carry more dust to be deposited, as it goes down, there would be less dust deposited. The net result would be the creation of layers. Of course, it is possible that both kinds of processes were at work on early Mars, but there is no way to distinguish these by examining images and other data from orbiting spacecraft alone.

Ultimately, geologists will have to go to Mars to investigate the changes in ancient martian environments recorded in these rocks.

These illustrations and the processes they portray were inferred from study of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images. The illustrations represent a synthesis of ideas described in the December 8, 2000, paper, "Sedimentary Rocks of Early Mars," in Science.

Artwork by Malin Space Science Systems;
Credit: NASA/JPL/Malin Space Science Systems


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