LINKING MULTIPLE COMPARISON FEATURES IN ONE TERRESTRIAL ANALOG: IMPLICATIONS FOR ROCK PROPERTIES, GEOLOGIC PROCESSES, FLUID HISTORY, AND POSSIBLE EXTRATERRESTRIAL LIFE ON MARS. Marjorie A. Chan1, Jens Ormö2, Chris H. Okubo3, Winston M. Seiler1 and Goro Komatsu4. 1Department of Geology & Geophysics, University of Utah (135 S 1460 E, Salt Lake City, Utah 84112 USA chan@earth.utah.edu). 2Centro de Astrobiología (INTA/CSIC), Instituto Na-cional de Técnica Aeroespacial (Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain). 3Lunar and Planetary Laboratory - University of Arizona (Tucson, AZ 85721). 4International Research School of Planetary Sciences, Università d’Annunzio (Viale Pindaro 42, 65127 Pescara, Italy).

Introduction: Recent, rich displays of surface features have been remotely imaged by the Mars Ex-ploration Rover (MER) Opportunity and the High Resolution Imaging Science Experiment (HiRISE) flying onboard the Mars Reconnaissance Orbiter (MRO) mission. These images provide valuable clues on extraterrestrial sedimentary, diagenetic, and weath-ering processes. Of important significance are the implications for water related processes on Mars [1] and thus the potential for extraterrestrial life [2]. Ter-restrial analogs provide groundtruth to constrain inter-pretations on the geologic history of Mars. The Juras-sic Navajo Sandstone of southern Utah and northern Arizona is remarkable in is its utility as a valuable ana-log for multiple, and possibly genetically connected features on Mars. Many of these analogous features can help unravel the significance of the past fluid his-tory and hydrodynamic regime, as well as surface weathering and eolian processes in prominent regions of Mars.

Analog Characteristics: Traits that the Navajo Sandstone shares with features recognized at Meridiani Planum (Figs. 1-3), Aram Chaos (Fig. 4), as well as in parts of the Valles Marineris system (Fig. 5) include: 1) iron oxide mineralogy and spheroidal geometries

preserved in concretions (“blueberries” of the Burns formation) [3, 4],

2) formation of ripples comprised of miniconcretions or “microberries” [5],

3) eolian stratification in sedimentary rocks, 4) distinctive small polygonal crack and microrelief

domal weathering patterns [6], 5) large or megapolygon cracks along significant

exposure surfaces, 5) preferentially cemented ridges and possible de-

formation bands, 6) bleaching along fractures and some concentric

bleaching patterns [7, 8], and 7) host rock and concretionary forms that may be

favorable sites to support and preserve microbial life [9].

Many of these characteristic physical traits are

linked to a relatively porous, homogeneous host rock that facilitates diagenesis and weathering, effects the

way fluids move through the sediment, and influences how the rock accommodates different physical stresses. Furthermore, an advantageous feature of the Navajo Sandstone is that it is widespread and has ex-quisite preservation of enhanced and etched relief fea-tures. In the desert regime, lateral and vertical extents can be studied and imaged without the interference of dense vegetation or overburden that can commonly obscure important features. For example, concretions commonly occur in numerous formations of many geo-logic ages worldwide, but there are few formations that can rival the range of distributions, and preserva-tion of entire chemical reaction fronts at different scales, as exposed in the Navajo Sandstone.

Fig 1. A. Surface lag accumulations of iron oxide concre-tions. A) Navajo Sandstone (~ 0.5-2 cm diameter) and b) Mars “blueberries” (<0.5 cm) imaged by the MER Opportu-nity, Sol 1103B Meridiani Planum, Mars (Pancam false color photo credit: NASA/JPL/Cornell).

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Although past geologic events in the history of the Mars depsits may differ, the modern exposure condi-tions of this terrestrial analog are also somewhat like the present Mars conditions. Current atmospheric moisture content (while different) is relatively low and thus allows wind as an important force in shaping the Martian surface while leaving a visible remnant re-cord.

Fig. 2. Microconcretions (~1-2 mm diameter) arranged in surface ripples and inset cross sectional views from (A) Ju-rassic Navajo Sandstone of Northern Arizona , and (B) Me-ridiani Planum imaged by the MER Opportunity, photo credit: NASA/JPL/Cornell) (Full picture from Pancam SOL 604 B Sequence 2534 and inset is Pancam stretched false color image, Sol 367B, Seq P2550).

Discussion: Understanding the past fluid history at a key locality such as Meridiani Planum requires examining a wide spectrum of features including geo-chemistry, geology, and geomorphology. Four exam-ples of features that are linked and/or occur together because of inherent properties or environmental setting are listed below. 1) Relatively porous homogeneous host rock transmits

advective and diffusive flow to allow diagenetic concretions, but may also facilitate tensile stresses in small polygon weathering cracks (Fig. 3) where there is not a strongly developed anisotropy.

2) Weathering factors combined with relative rock hardnesses and cementation are exhibited by the subtleties in erosion resistance (e.g., softer host rock vs. harder, better cemented concretions, with resulting “blueberry” accumulations, Fig. 1), and il-

lustrate the wind power needed to form loose “mi-croberry” concretion ripples (Fig. 2).

Fig. 3. A. Nested and superimposed scales of polygonal cracks and microrelief “cauliflower”-like weathering in the Jurassic Navajo Sandstone. B. Similar polygonal cracks in the Wopmay rock imaged by the MER Opportunity, Endur-ance Crater area of Meridiani Planum (Pancam false color photo credit: NASA/JPL/Cornell). 3) Layered sediments and stratification may be linked

to lithologic boundaries, fractures, or joint patterns that might act as fluid conduits for bleaching or cementation (Fig 4A, C, D). Such fluid pathways may display physical or chemical expressions of water-mobilized mineral asemblages such as sul-fates and iron oxides, or other mineral alteration patterns.

4) In a comparitive study of Mars Orbiter Camera (MOC) images [7], co-occurrences of hematite de-posits were reported with possible wind-erosion pits in apparently relatively weak, bright-colored layers (Fig. 4A, B), in addition to observable bleaching/cementation along fractures (Fig. 4C, D) at Meridiani Planum and Aram Chaos. Such trends have been extended with more detailed HiRISE im-ages that further document bleached halos in light-toned layered deposits in Valles Marineris [8] and elsewhere (Fig. 5). These new studies offer further insight into the mechanics and chemistry of re-gional, fracture-controlled, paleo-fluid flow through the sedimentary bedrock.

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Figure 4. Illustrations and interpretations from Ormö et al. [2004]. A. Bleached layers and wind erosion pits in Entrada Sandstone, Lake Powell, Utah. Lateral width of picture ~ 400 m. Photo credit: D. Netoff B. Strata bound pits in bright-colored deposits in Meridiani Planum. C. Bleached fault trace near Moab, Utah. Photo credit: W.T. Parry. D. Bright ridges in Meridiani Planum possibly due to cementa-tion/bleaching along fractures. The Navajo Sandstone contains relationships be-tween multiple traits, and while not all features are totally or perfectly analogous to Mars in every respect, there are sufficient parallels to show comparitive simi-larities and differences. In some cases, the differences can contribute to understanding why there is variabil-ity and what parameters might control or “pull” an Earth or Mars setting towards different or unique con-ditions. It is also likely that as new and/or more de-tailed images are released, other analogous features might be recognized and related to the hematite and bleaching occurrence as part of the fluid history. While chemically distinct from the layered deposits observed by Opportunity in Meridiani Planum [10], the Navajo Sandstone serves as an exceptional physical analog for interpreting the history of fluids on Mars. Conclusions: The desire to understand features on Mars can help drive efforts to better understand acces-sible Earth analogs, and encourage modeling or labora-tory tests that can be scaled up. The combination of terrestrial and planetary geology is opening up new interdisciplinary collaborations and directions that are strengthening both Earth and planetary sciences. Earth systems are dominated by water, and thus the analo-gous parallels offer tantalizing glimpses at the possi-bilities for discovering extraterrestrial life in the Mars

record. Terrestrial analogs provide key constraints and a comparative framework to Martian parameters be-cause characteristics observed remotely may imply certain host rock properties, hydrodynamic regimes, and sedimentary, diagenetic, and weathering proc-esses. The utility of the Jurassic Navajo Sandstone as an analog to Mars is multifold, and it is clear that con-tinued investigations of the Navajo Sandstone will lead to more fruitful insights on geologic processes on both Earth and Mars.

Figure 5. Fluid alteration along joints. A. Iron precipitation along joints in Navajo Sandstone, San Rafel Swell, Utah. B. Joints in Etched Terrain, Northern Meridiani Planum. Bed-rock along the joints is lighter in tone than the surrounding rock. This may be a result of chemical belaching of dark-toned minerals from the bedrock (Fig. 4c), cementation, or both. The wallrock along some joints is darker than the sur-rounding bedrock (diagonal lineations in the upper right quadrant), suggesting precipitates of dark-toned minerals along these fractures (HiRISE false color image). Acknowledgments: This work is supported by the National Aeronautics and Space Administration (to Chan) under grant NNG06GI10G issued through the Mars Fundamental Research Program. The work by

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Jens Ormö is supported by the Spanish Ministry for Science and Education (reference CGL2004-03215/BTE) The work by Chris Okubo is supported in part by a grant from NASA’s Mars Data Analysis Pro-gram (05-MDAP05-0002). References: [1] Squyres S.W. et al. (2004) Science 306, 1709-1714 [2] Squyres S.W. and Knoll A.H. (2005) EPSL 240, 1-

10. [3] Chan M.A. et al. (2004) Nature 429, 731-734. [4] Chan M.A. et al. (2005) GSA Today 15, 4–10. [5] Seiler W.M. et al. (2007) 38th LPSC, Meeting Ab-

stract 2076. [6] Chan M.A. et al. (2007) 38th LPSC Meeting Ab-

stract 1398. [7] Ormö J. et al. (2004) Icarus 171, 295-316. [8] Okubu C.H. and McEwen A.S. (2007) Science 315,

983-985. [9] Souza-Egipsy V. et al., Astrobiology 6, 527-545. [10] McLennan, S.M., et al. (2005) Earth Planetary

Sci. Letters 240, 95-121

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