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A. N. Crane (Agnes Scott College), E. F. Albin (Fernbank Science Center)
Schiaparelli basin is an ancient 470-km impact structure found in the eastern Terra Meridiani region of Mars. Observed along the interior margins of this basin are sequences of layered deposits that occur within material mapped as smooth plains. In places, over a dozen distinct layers are identified on high resolution Global Surveyor MOC images, with individual layer thicknesses ranging between 10 - 25 m as determined from MOLA data. Although these sediments may have been emplaced as an air fall deposit (i.e., volcanic ash or aeolian dust) [e.g., 1], evidence suggest that such layers may have been deposited in an aqueous environment - one characterized by alternating periods of deposition and non-deposition . Since Schiaparelli is a closed basin, it could have served as a lake reservoir during early Martian history when environmental conditions were suitable for supporting seas of water . If this were the case, then layered sediments may have formed insitu. Such a lacustrine setting could have produced the observed layering by way of the deposition of limestone. Although carbonate material may have been deposited through a purely chemical process, its presence is intriguing for its paleobiological implications since, as on Earth, the accretion of shells and other hard parts of marine organisms produce some forms of this rock. Ongoing research includes the analyses of Odyssey THEMIS data, in conjunction with morphologic evidence, in an attempt to detect the presence of carbonate deposits within the Schiaparelli basin.
References:  B. A. Hynek et al. (2002), LPSC, 33, 1408.  M. C. Malin and K. S. Edgett (2000), Science, 290, 1927-1936.  N. A. Cabrol and E. A. Grin (2001) Icarus, 149, 291-328.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.