WHAT CAN BE DEDUCED ABOUT THE CAPPING UNIT OF MARTIAN ‘INVERTED CHANNELS’ FROM THEIR THERMOPHYSICAL PROPERTIES?
Using thermal inertia derived from 2001 Mars Odyssey Thermal Emission Imaging System (THEMIS) data, we assessed the relative thermal inertia difference of FSR compared to the surrounding terrain. The thermophysical contrast for twenty large ‘inverted channels’ on Mars are often similar to well-indurated plains units. Where friable units are present, the FSR exhibit an elevated thermophysical contrast. We find few instances of depressed thermophysical contrast, as would be predicted for gravel-armored surfaces. These cases are explained by mantling overburden or aeolian ripples sourced from weathering of FSR materials.
The thermal signature, together with regional geology and morphology attributes, leads us to disfavor clast armoring as an induration agent for most martian FSRs. The available evidence is consistent with cementation as the most likely induration agent for FSRs, although lava-infilling is a plausible explanation especially for instances of nearby volcanic edifices. FSR cementation, probably by near-surface, solute-rich groundwater, extends aqueous processes beyond the period of widespread fluvial activity. Future work on the temporal response of the surfaces of inverted channels has the potential to further test the inferred induration mechanism and potentially constrain the grain size distribution.