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W. K. Hartmann, D. C. Berman, D. A. Crown, E. Turtle (Planetary Science Institute)
We have continued to work on updating the system of isochrons used to date Martian surface units. The system is based on known lunar cratering rates and use of calculated Mars/moon impact ratios to get Martian cratering rates and absolute ages [1, 2]. The new iteration combines Hartmann data on the shape of the production size distribution at larger diameters D (> 1 km) with Neukum data on the steep branch at smaller diameters.
This gives an improved fit of the calculated isochrons to the observed size distribution of craters on various Mars units. The results are in beautiful agreement with Mars meteorite data on widespread lava flows with ages of a few hundred MY. The results also continue to affirm very young lava flows and water flows in some areas, such as Elysium and the Cerberus plains (age < 100 MY; possibly < 20 MY) .
Continued examination of images and new crater counts show numbers of very young surfaces on debris aprons and glacier-like features which are found in Noachian cratered uplands at mid-to-high southern latitudes. These appear to be results of ongoing ice flow. Iceflow-like features have also been found in association with Malin and Edgett gullies (4). We have documented identical gullies from the air and on the ground in Iceland (4). Martian cratered uplands may have abundant ice deformation processes, though timescales and mechanisms still involve many unsolved problems.
References:  Hartmann, W. K., and G. Neukum 2001. Cratering chronology and evolution of Mars, in Chronology and Evolution of Mars, Eds. R. Kallenbach, J. Geiss, and W. K. Hartmann. (Bern: International Space Science Institute; also Space Sci. Rev., 96), pp. 165-194.  Ivanov, B. 2001. Mars/Moon cratering rate ratio estimates, in Chronology and Evolution of Mars, Eds. R. Kallenbach, J. Geiss, and W. K. Hartmann. Kluwer Academic Publishers, Netherlands, pp. 87-104.  Berman, D. C., and W. K. Hartmann 2002. Recent Fluvial, Volcanic, and Tectonic Activity on the Cerberus Plains of Mars. Icarus, in press.  Hartmann, W. K., T. Thorsteinsson, and F. Sigurdsson 2002 Martian Hillside Gullies and Icelandic Analogs. Submitted to Icarus.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.