Mathematics – Probability
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p32a03s&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P32A-03
Mathematics
Probability
5415 Erosion And Weathering, 5420 Impact Phenomena (Includes Cratering), 5470 Surface Materials And Properties
Scientific paper
Viking and now MGS document a complex eolian depositional history across Mars. This history includes thick unconformable deposits at all elevations, most similar to loess deposits on Earth. One of the oldest continuous sequences of loess on Earth is found in Argentina (perhaps as old as 12Ma). These sequences provide important clues for recognizing similar sequences on Mars and reveal the interplay with a long exposure to the impact flux. The Pampean Formation in Argentina is a loessoid deposit exhibiting a mixture of paleosols, alluvial fill, and dust. The Pampean Formation contains resistant layers reflecting precipitation of magnesium and calcium carbonates. Since they are nearly flat lying, outcropping resistant layers may resemble fluvial deposits. Four layers of impact glass have now been discovered within the Pampean Formation (only a few thousand years, 460 Ka, 3.3 Ma, and 10 Ma) within the loessoid deposits and provide a new perspective for the generation of glassy materials from porous substrates. The Argentine loessoid deposits closely resemble the extensive unconformable deposits across Mars, although the specific causes for sedimentary trapping may differ. Erosion of thick (100m to 1 km) deposits has exposed light and dark-colored avalanches. Some of the greatest concentrations of such streaks can be directly correlated with probable impact materials emerging from pedestal crater ejecta, analogous to exposures in Argentina. Because the impact record for the Martian deposits is at least 300 times longer than the Pampean Formation, accreted and archived impact materials are much more likely. Assessment of the missing cratering record in such regions reveals that layers of impact glass should not only be associated with nearby craters but also dispersed in the sections as isolated concentrations. The unusually long record of deposition on Mars challenges our terrestrial view of loess sequences as just recent (Pleistocene to Pliocene) veneers. The probability of stacking impact materials in such sequences through time requires a new perspective on their generation, survival, and dispersal. This perspective may provide new interpretations for the nature of Martian materials, including the mobile dark veneers and dark circumpolar dunes.
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