DECODING SURFACE MORPHOLOGIES FROM A CONTINENTAL SABKHA (WESTERN SAHARA, MOROCCO) RELATED TO THE INTERACTION BETWEEN MICROBIOTA AND THE PRECIPITATION OF CARBONATES AND EVAPORITES

In wind deflation areas of the Atlantic coast of Western Sahara (Morocco) modern sabkhas with large, flat-bottomed and steep-walled depressions, and a negative elevation (above mean sea level) have the evaporation of salty groundwater as the only agent leading to precipitation and accumulation of salt crusts. In one of these sabkhas, placed at about 15 km from the Atlantic Ocean, different sub-environments are determined by groundwater that permanently feeds streams, water ponds, and a waterfall produced by a vertical cliff. These contiguous, very confined habitats allow investigating a number of surface micro-morphologies whose formation is either still on-going or fully formed and mineralized, and, consequently, ready to be delivered to the fossil record. Such morphologies are the product of the interaction between mat-forming microbial communities and different mineral precipitations (carbonates and evaporites) determined by bio-induced, small-scale environmental changes, the evaporation of groundwater, and the effect of spray-water coming from the nearby waterfall. Because (bio)chemically-precipitated, continental carbonates (and evaporites) work as geo-archives of morphologies, and since modern sabkhas are widely recognized as Earth analogues to Martian paleoenvironments, their decoding (i.e. understanding the origin of micro-morphologies and the relationships that might exist with biota) can be a useful tool for identifying morphological biosignatures