HiRISE Observations of the Mars North Polar Layered Deposits

Details HiRISE Observations of the Mars North Polar Layered Deposits HiRISE Observations of the Mars North Polar Layered Deposits

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p33a1011f&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P33A-1011

Other

0726 Ice Sheets, 0758 Remote Sensing, 5416 Glaciation, 5462 Polar Regions, 6225 Mars

Scientific paper

We present the latest results of our observations of the martian north polar layered deposits at high resolution using MRO HiRISE. The NPLD can be divided into two different sections, based on the presence or absence of fracturing. The lower section is ubiquitously fractured, for unknown reasons, on the portions exposed in marginal scarps. The upper section lacks this extensive fracturing and comprises most of what is exposed in trough walls. Fracturing of the lower section may be pervasive, given the change in radar characteristics observed by SHARAD at approximately the boundary between the upper and lower sections. Preliminary analysis of HiRISE color data within the upper section shows that color differences between layers may exist. However, most images show these layers to be covered by frost and dust, masking their inherent albedo and making it difficult to distinguish individual layers from one another. This dust and frost cover hides thin layers; HiRISE has only observed layers at scales down to the limit of resolution in places where the slopes are relatively steep, indicating that all layers are being resolved on more typical slopes. The texture and morphology of a layer appears highly dependant on the style and extent of erosion, which, in turn, depends on the location of the NPLD outcrop. For example, by comparison with nearby MOC images used for previous layer correlations, we have identified the well-known "marker bed" in several HiRISE images; its only defining characteristic appears to be its resistance to erosion. Within one HiRISE image, we have identified several other layers that closely resemble the appearance of the original marker bed in that image, possibly indicating a major, repeating climate signal. No definitive evidence of ductile layer deformation has been discovered, other than possible soft-sediment deformation of the overlying dust lag. Examination of HIRISE images containing previously mapped faults confirms that these features are the result of brittle deformation. HiRISE observations of the north polar basal unit show that deposit to be interbedded sand and fractured ice. We suggest that the lower, fractured section of the NPLD was deposited when the sand supply feeding parts of the basal unit was exhausted (and/or average obliquity decreased) and that the upper section was emplaced during mid-range average obliquity conditions. An unconformity likely exists between the two sections, and the timing of the fracturing is unknown

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