Clay minerals in delta deposits and organic preservation potential on Mars

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Abstract

Clay-rich sedimentary deposits are often sites of organic matter preservation1,2, and have therefore been sought in Mars exploration3. However, regional deposits of hydrous minerals, including phyllosilicates and sulphates4,5, are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early Mars6,7,8. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)9 has recently identified phyllosilicates10 within three lake basins with fans or deltas that indicate sustained sediment deposition: Eberswalde crater7,11,12, Holden crater12,13 and Jezero crater14. Here we use high-resolution data from the Mars Reconnaissance Orbiter (MRO) to identify clay-rich fluvial–lacustrine sediments within Jezero crater, which has a diameter of 45 km. The crater is an open lake basin on Mars with sedimentary deposits of hydrous minerals sourced from a smectite-rich catchment in the Nili Fossae region. We find that the two deltas and the lowest observed stratigraphic layer within the crater host iron–magnesium smectite clay. Jezero crater holds sediments that record multiple episodes of aqueous activity on early Mars. We suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material.

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Figure 1: Mineralogy and extent of the Jezero crater watershed.
Figure 2: MRO view of Jezero crater.
Figure 3: CRISM spectra compared with library9 mineral reflectance spectra.
Figure 4: Topography and stratigraphy of Jezero basin.

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Acknowledgements

Special thanks go to the entire MRO team: without their ongoing efforts, these new discoveries would not be possible. We especially recognize the efforts of the CTX and HiRISE teams for coordinated observations with CRISM. Special thanks to Gregg Swayze for numerous discussions on interpreting CRISM spectra from the Nili Fossae region. The comments of reviewers Vincent Chevrier and Victor Baker helped improve this manuscript.

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Correspondence to Bethany L. Ehlmann.

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