New Insights into Gemina Lingula of the Northern Polar Layered Deposits, Mars from SHARAD Observations

Details New Insights into Gemina Lingula of the Northern Polar Layered Deposits, Mars from SHARAD Observations New Insights into Gemina Lingula of the Northern Polar Layered Deposits, Mars from SHARAD Observations

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p24a..08h&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P24A-08

Computer Science

Sound

0726 Ice Sheets, 0738 Ice (1863), 5462 Polar Regions, 5494 Instruments And Techniques, 6225 Mars

Scientific paper

The Shallow Radar (SHARAD) instrument on Mars Reconnaissance Orbiter expands our ability to study internal features of the Polar Layered Deposits (PLDs) by complementing optical and spectral imagery in addition to radar sounding by MARSIS on Mars Express. The theoretical vertical resolution is approximately 8 m in water ice. Horizontal resolution is 0.3 1 km along-track and 3 6 km across track. We present results of SHARAD over the northern PLD (NPLD) with an emphasis on layer character in Gemina Lingula, the NPLD lobe that extends along the southern edge of Chasma Boreale. Initial observations show two distinct units, an upper unit approximately 600 m thick exhibiting many strong radar reflectors with extensive lateral continuity, and a lower unit that is typically over 1 km thick with fewer and weaker reflectors that also appear to be continuous over large distances. Angular unconformities are evident between the units. These radar-defined units likely correspond to a smooth upper PLD unit and a lower, polygonally cracked PLD unit as observed in HiRISE imagery. Both would therefore make up the "finely layered unit" of Byrne and Murray (2002; JGR). A diffuse radar reflector underlies these units and is presumably the contact with the Vastitas Borealis Formation. If this interpretation proves correct, there is no significant "platy unit" of Byrne and Murray (2002) or "basal unit" of Fishbaugh and Head (2005; Icarus) existing under Gemina Lingula. After importing over 50 SHARAD data passes with over 300 crossovers into a seismic data interpretation package, we have interpreted radar reflectors as discrete horizons in order to map interface continuity and determine radar-detected layer thicknesses across the extent of Gemina Lingula. These results provide a 3-dimensional, first-order look at past accumulation patterns (and possibly the effects of flow) assuming that these radar interfaces are isochrones. Some evidence for brittle deformation is seen, particularly near Chasma Boreale. The geometrical relationships of radar horizons with Chasma Boreale and the spiral troughs are also examined in order to constrain the relative timing of their formation with respect to the deposits themselves.

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