Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p32a..01f&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P32A-01
Mathematics
Logic
5420 Impact Phenomena (Includes Cratering), 5470 Surface Materials And Properties, 5499 General Or Miscellaneous, 6225 Mars
Scientific paper
Buried impact basins revealed by MOLA elevation data have been found in both the lowlands and highlands of Mars, and provide evidence for older subsurface layers with a significant and recoverable history of cratering. If similar evidence were found in the very oldest geologic units on Mars, it would suggest that the surface materials in even the most densely cratered areas did not date from 4.6Gya but were somewhat younger. The Early Noachian is an open-ended stratigraphic period because until now it was not known whether a recoverable earlier history did exist on Mars. To address this issue we searched very high resolution MOLA data for the Nh1 unit (Hellas rim material) which on the east side of Hellas comprises over 1.2 million square kilometers and is the largest occurrence of Early Noachian terrains on Mars. We found clear evidence for Quasi-Circular Depressions (QCDs) larger than 25 km diameter that are not visible on Viking imagery and which we believe may be buried impact basins. This is supported not only by their topographic characteristics but also by their cumulative frequency curve: both visible and hidden features have similar curves that follow -2 power law slopes on a log-log plot. Contrary to our experience for larger QCDs in Middle Noachian and younger terrains elsewhere on Mars, the cumulative number of hidden basins at all diameters is less than that for the visible basins. But the contribution of hidden basins is significant: the total cumulative population (hidden plus visible) in Nh1 is roughly 1.6 times the visible population. While this is clear evidence for a surface somewhat older than that exposed at the surface, the number of buried basins is not so large as to suggest the buried surface is very much older than the oldest surface units. Comparison with studies done in Middle Noachian terrains suggest that the total populations of QCDs (visible and hidden) are nearly the same in both Early and Middle Noachian units. If true elsewhere on Mars, it may be that both units actually have the same population of craters but what appears to be a younger terrain does so because more of the craters are buried.
Frey Erin L.
Frey Herbert V.
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