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

The richness of information regarding climate, hydrology and sedimentary de position acquired from lakes and lacustrine environments makes them among t he most valuable targets for the Mars exploration. Moreover, terrestrial la custrine deposits record a large variety of biological traces and, thus, th ey are high potential candidates for exobiology study on Mars as well. Pale olakes have been recognized in several settings and ages on the Martian sur face. Crater lakes formed by channels debouching into impact craters are mo re common and characteristic than the lakes in open topographic basins. On the basis of the morphological characteristics of crater lakes we studied a long with theoretical models, we suggest that two types of lacustrine basin s could have occurred: deep-water lakes and dry lakes. Deep-water lakes sho w terraces at their rims, Gilbert-type deltas at the mouth of inflowing cha nnels, and a flat uniform floor. Dry lakes are dry for most of the time all owing chemical sediment accumulation. Evidence for this type of lakes is ve ry rare an Mars but the high albedo tone of some deposits suggests their pr esence. Mineralogical analysis is needed in order to identify this kind of deposits. The sedimentary facies and lithology associated with these two ty pes of lakes are different and they have important implications for drillin g operations at the landing sites. We describe the geological setting far e ach of these two types of lakes and their potential for the exobiology expl oration. (C) 2000 Elsevier Science Ltd. All rights reserved.