Sources of Clay-Rich Sediment in Eberswalde Crater, Mars With Implications for Biopreservation Potential

The Eberswalde crater paleolake system on Mars is home to an intact source-to-sink fluvial system where a catchment terminates in a river delta deposit. Through analysis of topographic and hyperspectral data from multiple geographic regions, we test the hypothesis that the smectites found within the Eberswalde deposit formed during the Noachian (i.e., >3.5 Ga) in the subsurface and are fluvial detritus transported during the Hesperian (i.e., 3.5-2.0 Ga). We find that the spectra from four pertinent regions (northwest Noachis Terra, Holden crater, and the Eberswalde watershed and delta deposit) are consistent with each other, and most consistent with Fe/Mg smectite clays, namely nontronite and saponite. This points to a detrital origin for the clays observed within Eberswalde crater. Analysis of the watershed also indicates that they likely formed within the subsurface, which previous studies suggest is the location most amenable to the preservation of evidence of past life on Mars. Furthermore, the presence of detrital clays, and not authigenic, indicates that the lake was similar to neutral-pH and a potentially habitable environment. Taken together, these observations indicate that: (a) within Eberswalde crater is a delta deposit that formed in a habitable environment, (b) that the deposit is composed of minerals that formed during the most habitable period in Mars' history, and (c) those minerals formed in an environment with strong potential to preserve evidence of life. Lastly, the similarities between the Eberswalde fluvial system and the Jezero system make it a compelling site as a standard of comparison by NASA's Perseverance Rover.