Paper No. 9
Presentation Time: 3:45 PM
EVIDENCE FOR LACUSTRINE CARBONATES AND CLAYS WITHIN MCLAUGHLIN CRATER, MARS
McLaughlin Crater is a large (~90 km diameter), ancient (> 3.7 Ga), deep (~2.5 km) impact crater on Mars. Along the eastern interior wall of the crater are a number of channels that terminate at an elevation ~500 meters above the modern crater floor. This observation could suggest the presence of a former base level at the surface of lake that once filled the crater. Also along the east interior of the crater is a broad terrace that might have formed from deposition of fluvial sediment into standing water. Within the floor of the crater are layered sediments that contain spectroscopic features similar to Mg-rich carbonates and Fe-Mg-rich clay minerals. In addition, impact ejecta from a younger, nearby crater (Keren Crater) deposited into Mclaughlin appears to have flow-like morphologies that are consistent with deposition in a wet environment. In fact, a number of possible debris flow units are present on the floor of McLaughlin. Finally, Keren’s ejecta are not altered where they are found outside of McLaughlin (based on thermal infrared spectroscopy), but are altered within the basin, below the proposed base level. Taken together, these observations point to the former presence of a lacustrine environment within McLaughlin Crater, which may have experienced episodes of rapid deposition that would be advantageous for the preservation of organic matter if any was present at the time. The source of the water within the crater could have been groundwater from the deep crust. McLaughlin Crater is among the most likely places to find evidence for groundwater-fed springs because the crater is deep and it occurs adjacent to the global topographic dichotomy boundary. The neutral-to-alkaline, Mg-Fe-rich fluids implicated by the mineralogy of putative lacustrine sediments are consistent with predicted fluid chemistry from groundwater that evolved in a basaltic crust. This site could provide access for exploration of a possible ancient, deep martian biosphere.