Martian paleolacustrine environments and their geological constrains on drilling operations for exobiological research

The richness of information regarding climate, hydrology and sedimentary deposition acquired from lakes and lacustrine environments makes them among the most valuable targets for the Mars exploration. Moreover, terrestrial lacustrine deposits record a large variety of biological traces and, thus, they are high potential candidates for exobiology study on Mars as well. Paleolakes have been recognized in several settings and ages on the Martian surface. Crater lakes formed by channels debouching into impact craters are more common and characteristic than the lakes in open topographic basins. On the basis of the morphological characteristics of crater lakes we studied along with theoretical models, we suggest that two types of lacustrine basins could have occurred: deep-water lakes and dry lakes. Deep-water lakes show terraces at their rims, Gilbert-type deltas at the mouth of inflowing channels, and a flat uniform floor. Dry lakes are dry for most of the time allowing chemical sediment accumulation. Evidence for this type of lakes is very rare on Mars but the high albedo tone of some deposits suggests their presence. Mineralogical analysis is needed in order to identify this kind of deposits. The sedimentary facies and lithology associated with these two types of lakes are different and they have important implications for drilling operations at the landing sites. We describe the geological setting for each of these two types of lakes and their potential for the exobiology exploration.