IAG Planetary Geomorphology Working Group

Featured images for July 2010:
Ancient sedimentary rocks in the Mawrth Vallis region, Mars

Images and caption contributed by Joe Michalski, Planetary Science Institute, Tucson, Arizona, USA, and Institut d'Astrophysique Spatiale, Université Paris-Sud, Orsay, France.

On Earth, the most ancient sedimentary rock record has been largely obliterated by plate tectonics and erosion. Remaining rocks from Earth's early history are severely deformed and geochemically overprinted by later events. Evidence for the earliest life on Earth found within these strata is often controversial because the rocks are so severely changed from their original state.

However, on Mars, extremely ancient sedimentary rocks are present in a relatively unmodified state. These materials probably hold clues to geological processes that were occurring early in the history of the Solar System. Many Martian sedimentary rocks contain evidence of clay minerals, which implies the former presence of a stable aqueous environment. Because the Martian sediments seemingly date to the same period when life was either forming or beginning to take hold on Earth, one must wonder if there could be evidence for life or pre-biotic chemistry contained within these ancient Martian sediments.



Image 1: Rugged, eroded terrain in the northwest portion of the image (north is up), and an eroded butte in the southeast contain rocks layered at the scale of decimeters to meters. Reddish-brown colors correspond to surfaces that are rich in nontronite - an Fe-rich smectite clay mineral. The bluish areas surrounding the butte in the central part of the image correspond to surfaces that are rich in hydrated silica and aluminous clay minerals (such as montmorillonite and kaolinite). In the south-central and eastern parts of the image, relatively flat, clay-rich terrain bears massive fractures at multiple scales. One set of fractures is found at the scale of 100s of meters and one at the scale of several meters. This type of geomorphology if found in association with many layered deposits on Mars, but it is particularly well developed here. Most likely, the fractures form in response to volume decrease associated with dehydration of expandable (smectite) clay minerals and other hydrated phases. [HiRISE image ESP_011383_2030]


The Mawrth Vallis region of Mars contains one of the largest exposures of phyllosilicate-bearing, sedimentary rocks on the red planet (Image 1-3). They were discovered initially using data from the Observatoire pour l'Eau, la Minéralogie, les Glaces, et l'Activité (OMEGA) instrument onboard the Mars Express spacecraft. Since that time, further work with OMEGA and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), as well as high-resolution imaging by the High-Resolution Imaging Science Experiment (HiRISE) and other instruments, have shown a diverse suite of clay minerals present within a thick (>150 m) layered, complex stratigraphic section (Images 1,2).



Image 2: Layering is particularly well exposed in this image. Here, we see 10s if not 100s of layers exposed in eroded topography. The fact that layers follow topography (i.e. follow along what would be imaginary topographic contour lines) indicates that the layers are relatively flat-lying. Layering itself is indicated by both color differences between units and by the response of the rocks to erosion; both slope-forming and cliff-forming layers are observed. The difference between these types of units could be due to differences in the fraction of clay minerals present between layers, degree of cementation, differences in grain size, or other physical-chemical differences inherent to the various units. [HiRISE image PSP_001929_2050]


The age of the Mawrth Vallis deposit is not known precisely - most of the stratigraphic section is extremely ancient (Mid-Late Noachian, ~3.6-4.1 Ga). The upper part of the section may have been re-worked by a later phase of aqueous processes, as suggested by apparent draping-relationships of units. This dates approximately to the timing of the Late Heavy Bombardment period in the Solar System, and may be an indication that Mars was a violent place, scarred by intense meteor impact flux during the time when the rocks formed. It also roughly coincides with the earliest evidence of life on Earth.



Image 3: CRISM band parameter maps (2.3 μm in red and 2.2 μm in green) overlain on a HiRISE image mosaic along with example CRISM spectra. The MSL landing ellipse for Mawrth Vallis is shown in black. HiRISE images include: ESP_011884_2045, ESP_012227_2045, ESP_012240_2045, ESP_012517_2045, PSP_005964_2045, PSP_006676_2045, PSP_007612_2045, PSP_008469_2040, PSP_009115_2040, PSP_009326_2040, PSP_010816_2040, and PSP_010882_2040). CRISM images include: FRT0000a600, FRT000089f7, FRT0000b141, FRT0000b643, and FRT0000bb59. (If this image is used for any purpose, please cite Michalski et al., paper submitted to Astrobiology.)[Full Resolution Image]


Future exploration of the Mawrth Vallis region from the Martian surface would reveal important new details about the mineralogy, geochemistry, texture, and organic chemistry of these deposits. This site is among the final group under consideration as a landing site for the Mars Science Laboratory (MSL) mission. If MSL lands on these clay-rich, layered deposits in 2012, it could revolutionize our understanding of aqueous geological processes and organic chemical processes that took place early in the history of the Solar System.

Further Reading:

Bishop JL, Dobrea EZ, McKeown NK, Parente M, Ehlmann BL, Michalski JR, Milliken RE, Poulet F, Swayze GA, Mustard JF and others. (2008) Phyllosilicate diversity and past aqueous activity revealed at Mawrth Vallis, Mars. Science, 321, 830-3. [Abstract]

Loizeau D, Mangold N, Poulet F, Ansan V, Hauber E, Bibring JP, Gondet B, Langevin Y, Masson P, and Neukum G. (2010) Stratigraphy in the Mawrth Vallis region through OMEGA, HRSC color imagery, and DTM. Icarus, 205, 396-418. [Abstract]

Loizeau D, Mangold N, Poulet F, Bibring J-P, Gendrin A, Ansan V, Gomez C, Gondet B, Langevin Y, Masson P and others. (2007) Phyllosilicates in the Mawrth Vallis region of Mars. J. Geophys. Res., 112, 1-20. [Abstract]

Malin MC, and Edgett KS. (2000) Sedimentary Rocks of Early Mars. Science, 290, 1927-1937. [Abstract]

McKeown NK, Bishop JL, Dobrea EZN, Ehlmann BL, Parente M, Mustard JF, Murchie SL, Swayze GA, Bibring J-P, and Silver EA. (2009) Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate. J. Geophys. Res., 114, 1-20. [Abstract]

Michalski, JR. and 13 others (in review). The Mawrth Vallis region of Mars: a potential landing site for the Mars Science Laboratory (MSL) mission. Astrobiology.

Michalski JR, and Fergason R. (2009) Composition and thermal inertia of the Mawrth Vallis region of Mars from TES and THEMIS data. Icarus, 199, 25-48. [Abstract]

Michalski JR, and Noe Dobrea EZ. (2007) Evidence for a sedimentary origin of clay minerals in the Mawrth Vallis region, Mars. Geology, 35, 951-954. [Abstract]

Noe Dobrea EZ. (in press) Mineralogy and stratigraphy of phyllosilicate-bearing and dark mantling units in the greater Mawrth Vallis / west Arabia Terra area: constraints on geological origin. JGR-Planets.

Poulet F, Bibring JP, Mustard JF, Gendrin A, Mangold N, Langevin Y, Arvidson R, Gondet B, and Gomez C. (2005) Phyllosilicates on Mars and implicatios for early martian climate. Nature, 438, 623-627. [Abstract]

Poulet F, Mangold N, Loizeau D, Bibring J-P, Langevin Y, Michalski J, and Gondet B. (2008) Abundance of minerals in the phyllosilicate-rich units on Mars. A&A, 487, L41-L44.

Wray JJ, Ehlmann BL, Squyres SW, Mustard JF, and Kirk RL. (2008) Compositional stratigraphy of clay-bearing layered deposits at Mawrth Vallis, Mars. Geophys. Res. Lett., 35, 1-6. [Abstract]

Past Images