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Bringing Cyclostratigraphy to Mars: Quasi-Periodic Bedding in Arabia Terra Sedimentary Deposits

Lewis, Kevin 1; Aharonson, Oded 1; Grotzinger, John P.1; McEwen, Alfred S.2; Kirk, Randolph 3; Suer, Terry-Ann 1
1 California Institute of Technology, Pasadena, CA.
2 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ.
3 Astrogeology Division, United States Geological Survey, Flagstaff, AZ.

Meter-scale topography of Martian layered deposits generated using stereo images from the High Resolution Imaging Science Experiment (HiRISE) permits unprecedented geometrically controlled stratigraphic studies. The widespread occurrence of light-toned stratified deposits within craters in Arabia Terra was first recognized from Mars Orbiter Camera (MOC) images. Typically, the occur as mounds on the crater floors which have been greatly eroded back from their original extent. In some cases, they are hundreds of meters in thickness, and composed of hundreds of parallel, 10-meter-scale beds. The occurrence of similar sedimentary deposits over such a large region of the planet implicates a common depositional process with relevance to planetary scale surface evolution. Using HiRISE stereo images we have derived one meter scale topographic maps of several sites in the western Arabia Terra region of the planet. These datasets permit stratigraphic investigation at the scale of the observed bedding. Through precise measurement of the structural tilt, the effects of tectonic deformation can be accounted for, allowing accurate reconstruction of the stratigraphic column. This process also removes the effect of the modern erosional topography, which can mask true stratigraphic thicknesses. At each of the four sites, we find the beds have remarkably consistent thicknesses, implying regular cyclicity in depositional conditions. At Becquerel crater, we also observe regular bundling of the bedding at a ~10:1 ratio. Given the scale of the bedding, we propose that astronomical cycles are responsible for the observed cyclicity. In particular, the obliquity of Mars is expected to significantly affect the volatile distribution, liquid water stability, and atmospheric pressure, with obvious implications for sediment transport and deposition. Given the difficulty of in-situ access, cyclostratigraphy is of great utility as a relative chronometer for the Martian rock record. Further, the simpler climate system of Mars relative to Earth makes it a natural laboratory for understanding the effects of astronomical variations on surface conditions.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009