Preservation of Organic Matter in Aqueous Deposits and Soils Across the Mars-Analog Qaidam Basin, NW China: Implications for Biosignature Detection on Mars

A variety of aqueous deposits and soils from gullies, fluvial channels, mountain slopes, alluvial fans, playas, polygons, and yardangs have been found on Mars. However, the occurrence of sedimentary organic matter (SOM) in these landscapes under hyperarid and strongly radiative conditions has yet to be fully assessed. With various desiccated landforms analogous to those on Mars, the Qaidam Basin in northwestern China is considered a promising hyperarid Martian analog. Here, aqueous deposits and soils from nine landforms across the extremely dry northwestern Qaidam and from four landforms across the dry southeastern Qaidam were sampled and investigated. Our results reveal that landform and moisture are important controls on organic carbon distribution across the Qaidam Basin, while sedimentary origin has a dominant effect in the extremely dry northwestern Qaidam. Combined with previous studies, low organic carbon contents of soils in the extremely dry northwestern Qaidam suggest possibly low rates of microbial carbon input and of organic carbon degradation in Mars-like environments. High organic carbon contents of aqueous deposits together with increasing trends along rivers indicate preservation of relic SOM and possibly slow degradation rates of organic matter as compared to their exposure timescale. Moreover, soils from the distal alluvial fan are found to favor the concentration of pedogenic organic carbon as compared to those from other landforms in the dry southeastern Qaidam and from all landforms in the extremely dry northwest. This suggests that subsoils in the distal fans are promising candidate targets for biosignature detection on Mars.