Microterracettes in Sabkha Oum Dba (Western Sahara, Morocco): physical and biological interactions in the formation of a surface micromorphology

Small-scale terracing (microterracettes) are surface geomorphic features that recur under a range of environmental settings, such as those existing in high to low temperature geothermal springs and in evaporitic environments, through the single or combined action of physicochemical agents and microbiological processes. Such morphology can also be observed in a confined sector of the Sabkha Oum Dba, an inland sabkha of the Western Sahara (Morocco), where field and laboratory investigations revealed that they primarilylargely depend on the accumulation of naviculoid diatoms. Through their ability of biofilm production these benthic diatoms are able to stabilize surface morphologies and make organic alveolar frameworks where precipitation of low-Mg calcite occur in areas subjected to active oxygenic photosynthesis. Because microterracettes arise in a specific set of environmental conditions, they have environmental significance and, thanks to a high fossilization potential due to mineral precipitation, they can be an effective source of bio-morphological and chemical evidence for life. The relationship with aqueous environments, considered to be widestread on Mars especially during a period of intense hydrologic activity as in the late Noachian and Esperian, make useful the understanding of surficial processes (such as the formation of microterracettes) whose formation is frequent in terrestrial analogs for Martian environments, such as ephemeral saline continental lakes (sabkhas), and related to products of bacterial and eukaryotic life, as in the case of biofilms, in search for similar life forms beyond Earth.