Meridiani on the Murray

Post by Dr. Jonathan Clarke

Soon after landing at Meridiani Planum the Opportunity rover imaged some curious wind erosion features. These were the haematite concretions commonly known as “blueberries” standing out from the substrate on stalks up to a cm or so in length. Good examples were seen at Eagle Crater, others were imaged at Fram Crater (Image 1). In places, the concretion has protected the underlying substrate from erosion. Sediments hosting the hematitic concretions have been eroded, leaving some concretions perched on small stalks. Several rocks at the Spirit landing site also show pedestals or fingers projecting away from rock surfaces.

Dedos on Meridiani Planum, Mars

Image 1: Two approximate true colour Pancam images of a boulder in Fram Crater, Meridiani Planum showing haematite concretions with a residual tail or stalk. The circular depression in the lower panel is from drilling by the RAT instrument. It is 45 mm in diameter. Top panel Sol085B_P2532_1. Credit: NASA/JPL/Cornell. Bottom panel image Sol088B_P2542_1. Credit: NASA/JPL/Cornell.

Similar features occur on Earth, and have been called “dedos” (Spanish for finger). They have been reported from the Sahara, Mojave, and Namib deserts and are typically formed in hard, fine-grained crystalline rocks, such as marble.

The Perry Sand Hills are a group of active, transverse, source bordering dunes near Wentworth, New South Wales, Australia, adjacent to the confluence of the Darling and Murray Rivers. Small yardangs of older, very weakly indurated sand are found in some swales. Classic dedos reminiscent of those on Meridiani, and also up to one centimetre in length occur on the upwind side of the yardangs (Image 2). Unlike those at Meridiani there is no distinct head to these features and the tips are composed of only slightly more cemented material than the unconsolidated sand which disintegrates back to loose sand with firm finger pressure. Their age is unknown, but it would seem questionable that they would survive a heavy fall of rain. Thus it is possible that they formed over a period of a few months.

It is planned to visit the Perry Sand Hills during a field trip prior to the International Association of Geomorphology Conference in Melbourne in 2009, along with other south eastern Australian landforms of interest to planetary scientists.

Dedos at Perry Sand Hills, NSW, Australia

Image 2: Dedos in eroded aeolian sand, Perry Sand Hills, southwestern New South Wales, Australia. Coin is 28 mm in diameter.


Further Reading:

Breed C. S., McCauley J. F. and Whitney M. I. 1989. Wind erosion forms. In: Thomas D. S. G. ed. Arid Zone Geomorphology, pp. 284-307. Belhaven Press, London.

Laity J. E. 1994. Landforms of aeolian erosion. In: Abrahams A. D. and Parsons A. J. eds. Geomorphology of Desert Environments, pp. 506-535. Chapman and Hall, London.

Lancaster N. 1984. Characteristics and occurrence of wind erosion features in the Namib desert. Earth Surface Processes and Landforms 9, 469-488. [Abstract]

McCauley J. F., Breed C. S., El Baz F., Whitney M. J., Grolier M. J. and Ward A. W. 1979. Pitted and fluted rocks in the western desert of Egypt: Viking comparisons. Journal of Geophysical Research 84, 8222-8232.

Sullivan, R., Banfield, D., Bell J. F. III, Calvin, W., Fike, D., Golombek, M., Greeley R., Grotzinger, J., Herkenhoff, K., Jerolmack, D., Malin, M., Ming, D., Soderblom, L. A., Squyres S. W., Thompson S., Watters W. A., Weitz C. M., and Yen A. 2005. Aeolian processes at the Mars Exploration Rover Meridiani Planum landing site. Nature 436, 58-61. [Abstract]

Thomas M., Clarke J. D. A. and Pain C. F. 2005. Weathering, erosion and landscape processes on Mars identified from recent rover imagery, and possible earth analogues. Australian Journal of Earth Sciences 52(3), 365-378. [Abstract]

Viles H.A., Bourke M.C. 2007. Weathering Features. In A Photographic Atlas of Rock Breakdown Features in Geomorphic Environments. Bourke M.C. and Viles H.A. (eds). Planetary Science Institute: Tucson; Pages 48-74. [Download]

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