Re: Subsurface radar mapping
Perhaps the iron-rich horizons could be correlated to Mars magnetic fields:
Magnetic map reveals ancient activity on the Red Planet.
Science News, Volume 155, Number 18 (May 1, 1999)
"The stripes of iron-rich rock on Mars have different magnetic orientations, he argues, because they solidified at different times. Each stripe represents a snapshot of the Martian magnetic field from a different epoch."
http://www.sciencenews.org/sn_arc99/5_1_99/bob2.htm
Then areas with high radar reflectivity but no indication of magnetic anomalies would be interpreted as due to carbonate.
Bob Clark